US20070265609A1 - Method for Ablating Body Tissue - Google Patents

Abstract

A cardiac ablation method including the following steps: inserting a treatment catheter into an atrium of a heart, the treatment catheter including an ultrasound emitter; positioning the ultrasound emitter to face heart tissue within the left atrium outside of a pulmonary vein; emitting ultrasound energy from the ultrasound emitter while rotating the ultrasound emitter about a rotation axis; and ablating heart tissue with the ultrasound energy to form a lesion outside of a pulmonary vein.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Application No. 60/747,137, filed May 12, 2006, and of U.S. Provisional Application No. 60/919,831, filed Mar. 23, 2007, the disclosures of which are incorporated herein by reference as if fully set forth.
INCORPORATION BY REFERENCE
• All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
FIELD OF THE INVENTION
• In this invention we describe a device and a method for creating ablation zones in human tissue. More specifically, this invention pertains to the treatment of atrial fibrillation of the heart by using ultrasound energy.
BACKGROUND OF THE INVENTION
• The condition of atrial fibrillation is characterized by the abnormal (usually very rapid) beating of left atrium of the heart which is out of synch with the normal synchronous movement (“normal sinus rhythm”) of the heart muscle. In normal sinus rhythm, the electrical impulses originate in the sino-atrial node (“SA node”) which resides in the right atrium. The abnormal beating of the atrial heart muscle is known as fibrillation and is caused by electrical impulses originating instead in the pulmonary veins (“PV”) [Haissaguerre, M. et al., Spontaneous Initiation of Atrial Fibrillation by Ectopic Beats Originating in the Pulmonary Veins, New England J Med., Vol. 339:659-666].
• There are pharmacological treatments for this condition with varying degree of success. In addition, there are surgical interventions aimed at removing the aberrant electrical pathways from PV to the left atrium (“LA”) such as the Cox-Maze III Procedure [J. L. Cox et al., The development of the Maze procedure for the treatment of atrial fibrillation, Seminars in Thoracic & Cardiovascular Surgery, 2000; 12: 2-14; J. L. Cox et al., Electrophysiologic basis, surgical development, and clinical results of the maze procedure for atrial flutter and atrial fibrillation, Advances in Cardiac Surgery, 1995; 6: 1-67; and J. L. Cox et al., Modification of the maze procedure for atrial flutter and atrial fibrillation. II, Surgical technique of the maze III procedure, Journal of Thoracic & Cardiovascular Surgery, 1995; 2110:485-95]. This procedure is shown to be 99% effective [J. L. Cox, N. Ad, T. Palazzo, et al. Current status of the Maze procedure for the treatment of atrial fibrillation, Seminars in Thoracic & Cardiovascular Surgery, 2000; 12: 15-19] but requires special surgical skills and is time consuming.
• There has been considerable effort to copy the Cox-Maze procedure for a less invasive percutaneous catheter-based approach. Less invasive treatments have been developed which involve use of some form of energy to ablate (or kill) the tissue surrounding the aberrant focal point where the abnormal signals originate in PV. The most common methodology is the use of radio-frequency (“RF”) electrical energy to heat the muscle tissue and thereby ablate it. The aberrant electrical impulses are then prevented from traveling from PV to the atrium (achieving conduction block within the heart tissue) and thus avoiding the fibrillation of the atrial muscle. Other energy sources, such as microwave, laser, and ultrasound have been utilized to achieve the conduction block. In addition, techniques such as cryoablation, administration of ethanol, and the like have also been used.
• There has been considerable effort in developing the catheter based systems for the treatment of AF using radiofrequency (RF) energy. One such method is described in U.S. Pat. No. 6,064,902 to Haissaguerre et al. In this approach, a catheter is made of distal and proximal electrodes at the tip. The catheter can be bent in a J shape and positioned inside a pulmonary vein. The tissue of the inner wall of the PV is ablated in an attempt to kill the source of the aberrant heart activity. Other RF based catheters are described in U.S. Pat. Nos. 6,814,733 to Schwartz et al., 6,996,908 to Maguire et al., 6,955,173 to Lesh; and 6,949,097 to Stewart et al.
• Another source used in ablation is microwave energy. One such device is described by Dr. Mark Levinson [(Endocardial Microwave Ablation: A New Surgical Approach for Atrial Fibrillation; The Heart Surgery Forum, 2006] and Maessen et al. [Beating heart surgical treatment of atrial fibrillation with microwave ablation.Ann Thorac Surg74: 1160-8, 2002]. This intraoperative device consists of a probe with a malleable antenna which has the ability to ablate the atrial tissue. Other microwave based catheters are described in U.S. Pat. Nos. 4,641,649 to Walinsky; 5,246,438 to Langberg; 5,405,346 to Grundy, et al.; and 5,314,466 to Stern, et al.
• Another catheter based method utilizes the cryogenic technique where the tissue of the atrium is frozen below a temperature of −60 degrees C. This results in killing of the tissue in the vicinity of the PV thereby eliminating the pathway for the aberrant signals causing the AF [A. M. Gillinov, E. H. Blackstone and P. M. McCarthy, Atrial fibrillation: current surgical options and their assessment, Annals of Thoracic Surgery 2002; 74:2210-7]. Cryo-based techniques have been a part of the partial Maze procedures [Sueda T., Nagata H., Orihashi K., et al., Efficacy of a simple left atrial procedure for chronic atrial fibrillation in mitral valve operations, Ann Thorac Surg 1997; 63:1070-1075; and Sueda T., Nagata H., Shikata H., et al.; Simple left atrial procedure for chronic atrial fibrillation associated with mitral valve disease, Ann Thorac Surg 1996; 62:1796-[800]. More recently, Dr. Cox and his group [Nathan H., Eliakim M., The junction between the left atrium and the pulmonary veins, An anatomic study of human hearts, Circulation 1966; 34:412-422, and Cox J. L., Schuessler R. B., Boineau J. P., The development of the Maze procedure for the treatment of atrial fibrillation, Semin Thorac Cardiovasc Surg 2000; 12:2-14] have used cryoprobes (cryo-Maze) to duplicate the essentials of the Cox-Maze III procedure. Other cryo-based devices are described in U.S. Pat. Nos. 6,929,639 and 6,666,858 to Lafintaine and 6,161,543 to Cox et al.
• More recent approaches for the AF treatment involve the use of ultrasound energy. The target tissue of the region surrounding the pulmonary vein is heated with ultrasound energy emitted by one or more ultrasound transducers. One such approach is described by Lesh et al. in U.S. Pat. No. 6,502,576. Here the catheter distal tip portion is equipped with a balloon which contains an ultrasound element. The balloon serves as an anchoring means to secure the tip of the catheter in the pulmonary vein. The balloon portion of the catheter is positioned in the selected pulmonary vein and the balloon is inflated with a fluid which is transparent to ultrasound energy. The transducer emits the ultrasound energy which travels to the target tissue in or near the pulmonary vein and ablates it. The intended therapy is to destroy the electrical conduction path around a pulmonary vein and thereby restore the normal sinus rhythm. The therapy involves the creation of a multiplicity of lesions around individual pulmonary veins as required. The inventors describe various configurations for the energy emitter and the anchoring mechanisms.
• Yet another catheter device using ultrasound energy is described by Gentry et al. [Integrated Catheter for 3-D Intracardiac Echocardiography and Ultrasound Ablation, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 51, No. 7, pp 799-807]. Here the catheter tip is made of an array of ultrasound elements in a grid pattern for the purpose of creating a three dimensional image of the target tissue. An ablating ultrasound transducer is provided which is in the shape of a ring which encircles the imaging grid. The ablating transducer emits a ring of ultrasound energy at 10 MHz frequency. In a separate publication [Medical Device Link, Medical Device and Diagnostic Industry, February 2006], in the description of the device, the authors assert that the pulmonary veins can be imaged and “a doctor would be able to electrically isolate the pulmonary veins by putting a linear lesion around them” (emphasis by inventors). It is unclear from this statement whether the ablation ring is placed around one single target vein, or around a plurality of veins. In the described configuration of the catheter tip, it can be easily seen that the described ring ultrasound energy source can only emit the ultrasound beam of a size to ablate only one pulmonary vein at a time.
• Other devices based on ultrasound energy to create circumferential lesions are described in U.S. Pat. Nos. 6,997,925; 6,966,908; 6,964,660; 6,954,977; 6,953,460; 6,652,515; 6,547,788; and 6,514,249 to Maguire et al.; 6,955,173; 6,052,576; 6,305,378; 6,164,283; and 6,012,457 to Lesh; 6,872,205; 6,416,511; 6,254,599; 6,245,064; and 6,024,740; to Lesh et al.; 6,383,151; 6,117,101; and WO 99/02096 to Diederich et al.; 6,635,054 to Fjield et al.; 6,780,183 to Jimenez et al.; 6,605,084 to Acker et al.; 5,295,484 to Marcus et al.; and WO 2005/117734 to Wong et al.
• In all above approaches, the inventions involve the ablation of tissue inside a pulmonary vein or at the location of the ostium. The anchoring mechanisms engage the inside lumen of the target pulmonary vein. In all these approaches, the anchor is placed inside one vein, and the ablation is done one vein at a time.
SUMMARY OF THE INVENTION
• One aspect of the invention provides a cardiac ablation system including an ablation catheter having an anchor adapted to support the ablation catheter within an atrium of a heart and an ultrasound emitter disposed radially outward from a rotation axis and from the anchor, and a control mechanism adapted to rotate the ultrasound emitter about the rotation axis and to provide ablation energy to the ultrasound emitter to ablate heart tissue. Some embodiments also include an ultrasound emitter support extending radially outward from the rotation axis and supporting the ultrasound emitter, which may be the a distal portion of the ablation catheter or may be a separate element.
• In some embodiments, the emitter is disposed to emit ultrasound energy through a distal end of the support, and in other embodiments the emitter is disposed to emit ultrasound energy radially outward from a side of the support. In some embodiments, the emitter is disposed at an angle greater than zero with respect to the outer surface of the support.
• In some embodiments, the emitter includes an ultrasound transducer and an ultrasound reflective surface disposed to reflect ultrasound energy from the transducer. The transducer may be disposed to direct ultrasound energy proximally toward the reflective surface.
• In some embodiments, the control mechanism is adapted to bend the emitter support at a desired angle from the rotation axis. This angle may be formed at a first location along the emitter support, with the control mechanism being further adapted to bend the emitter support at a second location along the emitter support.
• In some embodiments, the ultrasound emitter support includes or serves as an electrode in electrical communication with the control mechanism and the anchor includes or serves as an electrode in electrical communication with the control mechanism.
• The control mechanism may be adapted to move the anchor within a left atrium. The anchor may extend substantially along the rotation axis, with the ablation catheter being adapted to rotate with respect to the anchor. Alternatively, the anchor may extend along an axis other than the rotation axis. In embodiments in which the system further includes a delivery sheath adapted to contain the ablation catheter, either the delivery sheath or the ablation catheter may have a port through which the anchor extends. Some embodiments also include a second anchor supporting the ablation catheter.
• In some embodiments, the emitter is distally and proximally translatable with respect to the anchor. In some embodiments, the emitter is supported by a transducer support extending radially outward from the rotation axis and is distally and proximally translatable with respect to the anchor.
• The anchor may be adapted to contact a heart tissue surface, such as the interior wall of the atrium or an interior surface of a pulmonary vein. Some embodiments have a delivery sheath surrounding the ablation catheter, and the anchor is expandable to contact a support catheter surrounding the ablation catheter.
• In embodiments in which the ultrasound emitter includes an ultrasound transducer, the system may also include a fluid source and a fluid flow path adjacent to the transducer. The system may also have a fluid exit port adjacent to the transducer and extending from the fluid flow path to the exterior of the ablation catheter. In embodiments in which the ultrasound emitter is disposed proximal to a distal end of the ablation catheter, the ablation catheter may also have a fluid chamber in communication with the fluid source, disposed between the ultrasound emitter and the distal end of the catheter, and in fluid communication with the distal end of the catheter. The fluid chamber may have a plurality of fluid exit channels formed in the distal end of the catheter.
• Some embodiments also have a distance sensor adapted to sense distance between the ultrasound emitter and a tissue surface. The ultrasound emitter and the distance sensor may both be an ultrasound transducer. Some embodiments may also have an ablation depth sensor. The ultrasound emitter and ablation depth sensor may both be an ultrasound transducer.
• Another aspect of the invention provides a cardiac ablation system including an ablation catheter having an ultrasound emitter and an ultrasound emitter support extending radially outward from a rotation axis and supporting the ultrasound emitter, and a control mechanism adapted to rotate the ultrasound emitter about the rotation axis and to provide ablation energy to the ultrasound emitter to ablate heart tissue and adapted to bend the emitter support at a desired angle from rotation axis. In some embodiments, the desired angle is formed at a first location along the emitter support, the control mechanism being further adapted to bend the emitter support at a second location along the emitter support.
• In some embodiments, the ultrasound emitter includes an ultrasound transducer, with the system further comprising a fluid source and a fluid flow path adjacent to the transducer. The system may also include a fluid exit port adjacent to the transducer and extending from the fluid flow path to the exterior of the ablation catheter.
• Some embodiments also have a distance sensor adapted to sense distance between the ultrasound emitter and a tissue surface. The ultrasound emitter and the distance sensor may both be an ultrasound transducer. Some embodiments may also have an ablation depth sensor. The ultrasound emitter and ablation depth sensor may both be an ultrasound transducer.
• Yet another aspect of the invention provides a cardiac ablation method including the following steps: inserting a treatment catheter into an atrium of a heart, the treatment catheter including an ultrasound emitter; positioning the ultrasound emitter to face heart tissue within the left atrium outside of a pulmonary vein; emitting ultrasound energy from the ultrasound emitter while rotating the ultrasound emitter about a rotation axis; and ablating heart tissue with the ultrasound energy to form a lesion outside of a pulmonary vein. In some embodiments, the positioning step includes the step of bending an ultrasound emitter support. In some embodiments, the positioning step includes the step of moving the ultrasound emitter parallel to the rotation axis. In some embodiments, the positioning step includes the step of anchoring the treatment catheter, such as against the heart wall or by placing an anchor against an atrial wall outside of a pulmonary vein or within a pulmonary vein. The anchoring step may also involve placing a plurality of anchors within a plurality of pulmonary veins and/or expanding an anchor within a support catheter.
• In some embodiments, the rotating step includes the step of rotating the treatment catheter about the anchor. The rotation may include the step of rotating the ultrasound emitter less than 360° around the rotation axis or rotating the ultrasound emitter at least 360° around the rotation axis.
• In some embodiments, the ablating step includes the step of forming a lesion encircling at least two pulmonary vein ostia. The method may also include forming a second lesion around two other pulmonary vein ostia, possibly forming a third lesion extending from the first lesion to the second lesion, and possibly forming a fourth lesion extending from the first, second or third lesion substantially to a mitral valve annulus.
• In some embodiments, the emitting step includes the step of transmitting ultrasound energy distally from a distal end of the treatment catheter and/or radially from the treatment catheter. In some embodiments, the emitting step includes the step of transmitting ultrasound energy from an ultrasound transducer (possibly in a proximal direction) and reflecting the ultrasound energy from a reflector. These embodiments may also include the step of rotating the reflector.
• Some embodiments include the step of passing fluid through the ablation catheter and through an exit port adjacent the ultrasound emitter. The fluid may pass into a fluid chamber disposed between the ultrasound emitter and the heart tissue.
• Some embodiments include the step of sensing distance between the ultrasound emitter and a tissue surface, such as by using the ultrasound emitter to sense distance between the emitter and the tissue surface. The distance sensing step may include the step of sensing distance between the ultrasound emitter and the tissue surface over an intended ablation path prior to the ablating step and may include the step of repositioning the ultrasound emitter as a result of sensed distance determined in the sensing step.
• Some embodiments include the step of sensing depth of ablation in the heart tissue, such as by using the ultrasound emitter to sense depth of ablation in the heart tissue. The speed of rotation of the ultrasound emitter and/or the power delivered to the ultrasound emitter may be based on sensed depth of ablation.
• Some embodiments include the step of sensing thickness of the heart tissue. The speed of rotation of the ultrasound emitter and/or the power delivered to the ultrasound emitter may be based on sensed tissue thickness. In some embodiments, the ablating step includes the step of forming a substantially elliptical lesion segment in the heart tissue.
• Still another aspect of the invention provides a cardiac ablation method including the following steps: inserting a treatment apparatus into an atrium of a heart, the treatment apparatus having an ultrasound emitter and an ultrasound emitter support; positioning the ultrasound emitter to face heart tissue within the left atrium outside of a pulmonary vein; emitting ultrasound energy from the ultrasound emitter while changing a bend angle in the ultrasound emitter support; and ablating heart tissue with the ultrasound energy to form a lesion outside of a pulmonary vein. In some embodiments, the positioning step includes the step of bending an ultrasound emitter support. In some embodiments, the positioning step includes the step of anchoring the treatment catheter.
• Some embodiments add the step of rotating the ultrasound emitter about a rotation axis during the emitting step. In some embodiments, the ablating step includes the step of forming a substantially linear lesion and/or a substantially elliptical lesion segment in the heart tissue.
BRIEF DESCRIPTION OF THE DRAWINGS
• The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:
• FIG. 1 shows the device including a catheter in one embodiment of the invention.
• FIG. 2 shows the construction of the shaft of the catheter in one embodiment of the invention.
• FIGS.3A-C show bending of a distal portion of the catheter ofFIG. 1.
• FIG. 3D shows bending of the distal end of the catheter ofFIG. 1 and an anchor mechanism.
• FIG. 4 shows the distal tip assembly of the catheter ofFIG. 1.
• FIG. 5 is a view of the device in a second embodiment.
• FIG. 6 shows the distal tip assembly of the catheter ofFIG. 5.
• FIG. 7 is a view of the device in a third embodiment.
• FIG. 8 shows the distal tip assembly of the catheter ofFIG. 7.
• FIG. 9 is a view of the device in a fourth embodiment.
• FIG. 10 shows the distal tip assembly of the catheter ofFIG. 9.
• FIG. 11 shows an ablation zone encircling four pulmonary veins and the device in one embodiment of the invention.
• FIG. 12 shows two ablation zones each around two pulmonary veins.
• FIG. 13 shows an ablation zone around three pulmonary veins.
• FIGS.14 to17 show various mechanisms for the anchoring a portion of the catheter.
• FIG. 18 shows yet another embodiment of the invention as positioned in the left atrium of the heart.
• FIG. 19 shows the use of the device ofFIG. 18 in the atrium of the heart.
• FIG. 20 shows the distal end of the device ofFIG. 18 beyond the guiding sheath.
• FIG. 21A shows the details of the transducer housing at the distal tip of the catheter.
• FIG. 21B shows the transducer mounting header with fluid flow channels.
• FIG. 21C shows an alternative design for the fluid pocket containment component.
• FIG. 22 is a view of the construction of the therapy catheter.
• FIG. 23 shows a view of the construction of the outer catheter.
• FIG. 24 is a view of the characteristics of the ultrasound beam as it exits from the transducer.
• FIG. 25 shows formation of the shape of an ablation lesion.
• FIGS.26 A-D show the development of the ablation lesion as function of time.
• FIGS.27 A-D show the interaction of the ultrasound beam with the tissue at various distances from the ultrasound transducer.
• FIGS.28 A-B are views of the interaction of the ultrasound beam with the tissue when the tissue is presented to the beam at an angle.
• FIG. 29 shows the effect of the movement of heart muscle during ablation.
• FIG. 30 shows the transmission and reflections of ultrasound beam from the target tissue.
• FIG. 31 shows position of the catheter set in the left atrium in a condition when it may not be desirable to create an ablation zone.
• FIG. 32 shows a catheter set designed to address the right pulmonary veins.
• FIG. 33 shows a lesion set according to one embodiment of this invention.
• FIG. 34 shows the creation of an ablation zone near the left pulmonary veins.
• FIGS.35A-C show the formation of a line lesion from the left pulmonary veins to the right pulmonary veins.
• FIG. 36 shows a vertical line of ablation ending at the mitral valve annulus.
• FIG. 37 shows the use of the device ofFIG. 31 in creating the ablation zone in the right pulmonary veins.
• FIGS.38 A-K show a variety of candidate lesion sets in the left atrium.
DETAILED DESCRIPTION OF THE INVENTION
• The invention described herein includes a device and methods for creating ablation zones in tissue. The device of the invention includes an elongated member (e.g., a catheter) and an anchor mechanism. The elongate member includes a distal tip assembly for directing energy to a tissue. Uses of the invention include but are not limited to providing a conduction block for treatment of atrial fibrillation in a subject, for example, in a patient.
• One aspect of a first embodiment of the invention is shown inFIG. 1. As shown, thedevice100 includes an elongate member that can be acatheter110. In other implementations, the elongate member is a cannula, tube or other elongate structure having one or more lumens. Thecatheter110 can be made of a flexible multi-lumen tube. As shown, thecatheter110 can include adistal tip assembly112 positioned at a distal portion of thecatheter110. Thetip assembly112 can house an energy delivery structure, for example, an ultrasound transducer subassembly114 (described in more detail in reference toFIG. 4).
• Although the ablation device described herein includes a distal tip assembly having an ultrasound transducer as a source of ablation energy, it is envisioned than any of a number of energy sources can be used with various implementations of the invention. Suitable sources of ablation energy include but are not limited to, radio frequency (RF) energy, microwaves, photonic energy, and thermal energy. It is envisioned that ablation could alternatively be achieved using cooled fluids (e.g., cryogenic fluid). Additionally, although use of a single ultrasound transducer is described herein as an exemplary energy delivery structure, it is envisioned that a plurality of energy delivery structures, including the alternative energy delivery structures described herein, can be included in the distal portion of the elongate member. In one implementation the elongate member is a catheter wherein the distal portion of the catheter includes multiple energy delivery structures, for example, multiple ultrasound transducers. Such a catheter distal portion can be deployable as a loop or other shape or arrangement to provide positioning of one or more of the energy delivery structures for a desired energy delivery.
• The elongate member of the device can include a bending mechanism for bending a distal portion of the elongate member (e.g., a catheter) at various locations (an example of such bending is shown in FIGS.3A-D). The bending mechanism can include but is not limited to lengths of wires, ribbons, cables, lines, fibers, filament or any other tensional member. In one implementation the bending mechanism includes one or more pull wires, for example, a distal pull wire and a proximal pull wire. A variety of attachment elements for connecting the bending mechanism and the elongate member are envisioned. As shown inFIG. 1, in one implementation where the elongate member is acatheter110, thedistal pull wire116 and thetransducer subassembly114 are secured to thetip assembly112 by means of a distaladhesive band118. Other means of attaching thedistal pull wire116 to a portion of thetip assembly112 include but are not limited to attachment using: adhesive, welding, pins and/or screws or the likes. Pullwire116 can be contained in a lumen (not shown) of thecatheter110 and can terminate at aslider120 in aproximal housing122. Theproximal housing122 can include various actuating mechanisms to effect various features of the catheter, as described below. In one implementation, theslider120 can move in aslot124 which pulls or pushes thewire116. Since the distal end of thewire116 is secured to thetip112, the result is that thecatheter tip112 can be bent and unbent as desired at adistal bend location126 by moving theslider120.Distal bend location126 can be positioned on thedistal tip assembly112 as needed to achieve the desired bending of thecatheter110.
• A second analogous bending mechanism can be provided in the catheter which is more proximally positioned with respect to the distal tip assembly. As shown inFIG. 1, aproximal pull wire128 can reside in a lumen (not shown) of thecatheter110 and thewire128 distal end can be secured in thecatheter110 by a proximaladhesive band130. Thisproximal pull wire128 can terminate in asecond slider132 at theproximal housing122. Theslider132 can move in asecond slot134 which allows thedistal tip assembly112 to be bent at aproximal bend location136.
• The elongate member can further include an anchor mechanism by which the distal portion of the elongate member can be held in a relatively predictable position relative to a tissue, for example, inside a chamber such as the left atrium of the heart. As shown inFIG. 1, in one implementation ananchor mechanism140 includes apre-shaped wire loop138. In a specific implementation, thewire loop138 is made of a shapeable wire, for example, made from a shape-memory material such as Nitinol (nickel-titanium alloy). Alternatively, the anchor mechanism can include a loop made from any of a number of materials such as metal, plastic and/or fiber or combinations thereof. Although a loop is described, it is envisioned that any of a number of shapes, curved and/or angular, two-dimensional and/or three-dimensional can provide the anchoring required. Theanchor140 can reside in a lumen (not shown) of thecatheter110, and can exit from thecatheter110 through anotch142 near the distal end of the catheter110 (seeFIG. 1). The proximal end of theanchor mechanism140 can terminate in athird slider148 at theproximal housing122. Thethird slider148 can move in athird slot150 at theproximal housing122, thereby producing a correspondinganchor mechanism movement144 of theanchor mechanism140.
• In one implementation, when theslider148 is in a proximal position, thewire loop138 can be maintained in a substantially linear shape inside the lumen of the catheter110 (not shown). In use, asthird slider148 is advanced distally in theslot150, a distal tip of thewire loop138 exits the notch142 (not shown). As theslider148 is further advanced, thewire loop138 can take on the shape of a pre-formed loop as it is unrestricted by the confines of a lumen (seeFIG. 3D). As shown inFIG. 1, thewire loop138 of theanchor140 can be advanced further until it makes a firm contact with the tissue such as theceiling wall146 of the left atrium of the heart. One function of thewire loop138 is to provide a firm contact and/or stabilization between theanchor mechanism140 and the tissue, and thereby between a region of thecatheter110 and the tissue (seeFIG. 1). An additional function of the anchor mechanism is to provide an axis around which all or a portion of the catheter shaft can be rotated. Such rotation of the catheter is illustrated inFIG. 1, asarrow152. As shown inFIG. 1, in one implementation arotation mechanism154, for example, a wheel, is provided at theproximal housing122 by which all or a portion of thecatheter110 shaft can be rotated around the axis defined by theanchor mechanism140. As can be easily envisioned, through rotational movement about such an axis, the most distal portion of thetip assembly112 can be swept in a desired path in relation to target tissue. In one implementation, the path of thetip assembly212 can be a substantiallycircular path262 inside a tissue chamber such as the left atrium of the heart (seeFIG. 11).
• A transducer subassembly can be secured in the distal tip assembly of the catheter. As shown inFIG. 1, in one implementation atransducer subassembly114 is secured by the distaladhesive band118. The transducer subassembly is described in more detail herein for various embodiments of the invention. In one implementation, thetransducer subassembly114 includes a temperature measuring device such as a thermistor or a thermocouple (not shown). The transducer can be energized by the wires which, along with the temperature sensor wires, can be contained in a lumen of the catheter (not shown). As shown inFIG. 1, such wires can terminate in a connector, for example, atransducer connector156 at theproximal housing122. Theconnector156 can be attached to and detached from a power generator and/or controller (not shown). It is envisioned that such a power generator and/or controller can energize the transducer, display temperature readings and perform any of a number of functions relating to such transducers as well understood in the art. For example, monitoring A-mode signal and the like (e.g., B-mode). In use, as the transducer is energized, it can emit anultrasound beam158 towards thetissue146. As the energy is transferred from the ultrasound beam into the tissue, the targeted tissue portion can be heated sufficiently to achieve ablation. Thus, as shown inFIG. 1, anablation zone160 can be created in the tissue.
• During the energizing of the transducer, the transducer may become heated. It is envisioned that the transducer can be maintained within a safe operating temperature range by cooling the transducer. In one implementation cooling of the transducer can be accomplished by contacting the transducer subassembly with a fluid, for example, saline. In some implementations the transducer can be cooled using a fluid having a lower temperature relative to the temperature of the transducer. In one implementation a fluid for cooling the transducer is flushed past the transducer subassembly from a lumen in the catheter (see e.g.,FIG. 2). Accordingly, as shown inFIG. 1, the proximal end of a lumen of thecatheter110 can be connected to afluid port162, for example, a luer fitting, in theproximal housing122. As further shown inFIG. 1, in one implementation fluid used for cooling the transducer can exit thecatheter tip112 through a one ormore apertures164. The apertures can be a grating, screen, holes, weeping structure or any of a number of suitable apertures. In oneimplementation apertures164 are drip holes.
• Referring toFIG. 2, in one implementation where the elongate member of the device is a catheter, the shaft of thecatheter110 includes amulti-lumen tubing170 having one ormore lumens176, which is encased in abraid166 of suitable metallic or non-metallic filaments and is encased in asmooth jacket168 made of conventional biocompatible material.Lumens176 can accommodate any of a number of features of the invention including but not limited to, pull wires, fluids, gases, and electrical connections.
• In FIGS.3A-C, an exemplary series of drawings illustrate bending of the catheter distal portion in more detail. In the implementation shown, thedistal pull wire116 is secured at a distal portion of thetip assembly112 by means of the distaladhesive band118. In use, as thedistal pull wire116 is pulled by moving the first slider120 (seeFIG. 1), the catheter distal portion is bent atlocation126 in thedirection172, thereby moving from position X to position Y, as shown inFIG. 3B. Next, theproximal pull wire128, which is secured in the catheter lumen at a position by proximaladhesive band130, is pulled by moving the second slider132 (seeFIG. 1). This results in thecatheter110 distal portion bending atlocation136 and moving in thedirection174 to position Z, away from the longitudinal axis of the catheter, as shownFIG. 3C.
• It is envisioned that the pull wire attachment points, and correspondingly the bend locations in the device can be configured, in any of a number of ways, not limited to the examples described herein. For example, it is envisioned that a single pull wire or other bend inducing mechanism can be used. Alternatively, the use of three or more such mechanism is envisioned. With respect to attachment points for bend inducing mechanism, it is envisioned that any location along the distal tip assembly as well as the catheter distal portion are suitable optional attachment points. With respect to the number and location of bend locations in the device, it is envisioned that a spectrum of suitable bend locations can be provided. For example, while one and two bends are illustrated herein, it is envisioned that three or more bends can be used to achieve a desired catheter configuration and/or application of energy using the device.
• Theanchor mechanism140 of the device can be deployed in a separate or simultaneous step from bending the device, as shown inFIG. 3D. Theanchor mechanism140, which can be configured to reside in a lumen (not shown) of thecatheter110, is advanced out of thecatheter110 and through theanchor notch142 by moving the third slider148 (seeFIG. 1). In the implementation shown inFIG. 3D, as theanchor mechanism140 exits the notch142 a distal portion of themechanism140 takes on the pre-formed shape of aloop138. Thisloop138 is advanced further inaxial direction144 until it firmly engages tissue, for example in the inside wall of a tissue chamber such as the left atrium of the heart. The anchor mechanism provides a rotational axis for the distal tip assembly. Thetransducer subassembly114 can be intentionally displaced away from this axis so that when the catheter shaft is rotated (see arrow152) around the axis provided by theanchor mechanism140, the transducer can traverse a substantially circular loop inside the tissue chamber. The result of this motion is to create a substantially circular ablation zone inside the tissue chamber (described in more detail inFIG. 11). It is envisioned that an arc-shaped or other curved ablation zone could alternatively be created with the device.
• The design of the distal tip subassembly can include a variety of configurations providing alternative means of delivering energy to tissue. A first embodiment of thedistal tip subassembly1112 is shown inFIG. 4. As illustrated, thetip assembly1112 can include a closedend tube casing1142 which is transparent to ultrasound waves. It can further contain atransducer subassembly1114 including anultrasound transducer1120. Thetransducer1120 can be made of a piezoelectric material such as PZT (lead zirconate titanate) or PVDF (polyvinylidine difluoride) and the like. Thetransducer1120 can be configured as a disc and the faces of the disc can be coated with a thin layer of a metal such as gold. In one implementation the disc is a circular flat disc. Other suitable transducer coating metals include but are not limited to stainless steel, nickel-cadmium, silver or a metal alloy. As shown inFIG. 4, in one implementation thetransducer1120 can be connected toelectrical attachments1130 and1132 at two opposite faces. These connections can be made ofinsulated wires1134 which can be, for example, a twisted pair or a coaxial cable so as to minimize electromagnetic interference. When a voltage is applied across the transducer,ultrasonic sound beam1158 is emitted. The frequency of the ultrasound beam is in the range of about 1 to 50 megaHertz.
• As shown inFIG. 4, atemperature sensor1136 can be coupled with thetransducer1120, for example, attached to the back face of thetransducer1120. The temperature sensor can be comprised of a thermocouple or a thermistor or any other suitable means. As shown inFIG. 4, thesensor1136 can includewires1138 which carry the temperature information to the catheter proximal end. Thewires1134 and1138 together can form awire bundle1140 extending to the catheter proximal end.
• As further shown inFIG. 4, thetransducer1120 can be attached to abacking1126 by means of anadhesive ring1122 or other attachment, which creates a void orpocket1124 between thetransducer1120 and thebacking1126. Thepocket1124 can include a material which efficiently reflects sound waves generated by thetransducer1120. The material of thepocket1124 can be air or any other suitable material such as metal or plastic which reflects the sound waves. Advantageously, the sound waves thus can be directed to exit from the front face of the transducer, resulting in a minimum amount of sound energy lost out through the transducer back face into the backing. The backing can be made of a thermally conductive material such as metal or plastic for aiding in the dissipation of heat which is created when the transducer is energized.
• As illustrated inFIG. 4, thewire bundle1140 can be fed through a passageway orhole1128 in thebacking1126 and can be housed in a lumen of thecatheter1110. The wire bundle can terminate in theconnector156 at the proximal housing122 (seeFIG. 1). As shown inFIG. 4, the proximal end of thebacking1126 can be secured to thecasing1142 by means of thedistal adhesive band1118. This creates a void orchamber1146 between the distal end of thecasing1142 and thedistal adhesive band1118. Thechamber1146 is configured to be filled with a thermally conductive fluid such as saline so that thetransducer1120 can be cooled while energized. Thedistal adhesive band1118 can include apassageway1148 which is used in connecting thechamber1146 to a fluid carrying lumen. Thepassageway1148 can be in fluid communication with thefluid port162 at theproximal housing122 through one of the lumens (not shown) of the catheter1110 (seeFIGS. 1 and 4). As shown inFIG. 4, thechamber1146 can include one ormore apertures1164, for example, drip holes distributed circumferentially at thechamber1146 distal portion. In use, prior to insertion of the device into the body, the chamber can be filled with a fluid such as saline. This can be accomplished using a suitable fluid supply device such as a syringe connected to the fluid port (not shown). The fluid from the syringe can flow through the passageway of the distal adhesive band, into the chamber while expelling the air out from the chamber through the apertures. During the use of the device in the body, a constant drip of saline can be maintained, if necessary, to cool the transducer.
• Still referring toFIG. 4, adistal pull wire1116 can be secured to thedistal tip subassembly1112 by thedistal adhesive band1118. Thedistal pull wire1116 can reside in one of thelumens1176 of thecatheter1110 and can be connected to theslider120 in the proximal housing122 (seeFIG. 1 andFIG. 4). As described above in reference toFIG. 3A, thedistal pull wire1116 can be utilized in bending the distal portion of thecatheter1110. As shown inFIG. 4, thedistal tip subassembly1112 can be securely attached to thecatheter tubing1170 of thecatheter1110 by theproximal adhesive band1144. As further shown inFIG. 4,lumens1176 of thecatheter tubing1170 can be utilized for passage of various elements of thetip subassembly1112 and any of their related features, in addition to instruments, gases, fluids, or other substances.
• A second embodiment of the invention including an alternative distal tip assembly arrangement is shown inFIG. 5. Here thetransducer subassembly1214 is mounted in thedistal tip assembly1212 such that theultrasound transducer1220 face is substantially parallel to the longitudinal axis of the catheter1210 (that is to say the longitudinal axis of thecatheter1210 before bending thedistal tip assembly1212 or catheter1210). In this configuration, thesound beam1258 exits from a lateral surface of thetip assembly1212. The construction of the catheter in this configuration can be essentially same as that described herein for the first embodiment (seeFIGS. 1-4).
• As shown inFIG. 5, thedistal tip assembly1212 andcatheter1210 bend points,distal bend location1272 andproximal bend location1274 respectively, can be arranged and configured such that theultrasound beam1258 is presented to thetissue146 in a substantially right angle from thecatheter1210 longitudinal axis. In this manner anablation zone1260 is produced laterally through thetip assembly1212.FIG. 6 shows details of thedistal tip assembly1212 for this embodiment. As illustrated, thetip assembly1212 can be assembled in atube1242 which is substantially transparent to the ultrasound waves1258. Thetransducer subassembly1214 can include atransducer1220 which haselectrical connections1230 and1232 on opposite flat faces. As discussed herein, thetransducer1220 can include atemperature sensor1236 on, for example, a back side which has wire connections. The transducer wires and the temperature sensor wires together form abundle1240 which resides in alumen1276 of thecatheter tubing1270.
• Still referring toFIG. 6, the distal end of thetube housing1242 can be sealed. As shown inFIG. 6, in one implementation the distal end is sealed with a thermally conductive adhesive1250. The back side of thetransducer subassembly1214 can be secured to anadhesive ring1222 that is connected to abacking1226. Thus, a void orpocket1224 is created between thetransducer1220 and thebacking1226. As shown inFIG. 6, thebacking1226 can be secured to the inner wall of thetube1242, for example, by thedistal adhesive band1218. There can be apassageway1248 in theadhesive band1218 to allow the flow of a fluid such as saline to be introduced into thechamber1246. Thepassageway1248 can be in fluid communication with thefluid port162 at theproximal housing122 of the catheter1210 (seeFIGS. 1 and 6). As discussed herein thechamber1246 can include a number ofapertures1264, for example, drip holes distributed circumferentially at thechamber1246 distal end. As further described herein, prior to insertion of the device into the body, thechamber1246 can be filled with a fluid such as saline. In addition, during the use of the device in the body, a constant drip of saline can be maintained, as required to cool thetransducer1220.
• Again referring toFIG. 6, adistal pull wire1216 can be secured to thedistal tip subassembly1212 by thedistal adhesive band1218. Thedistal pull wire1216 can reside in one of thelumens1276 of thecatheter1210 and can be connected to theslider120 in the proximal housing122 (seeFIG. 1 andFIG. 6). As described above in reference toFIG. 3A, thedistal pull wire1216 can be utilized in bending the distal portion of thecatheter1210. As shown inFIG. 6, thedistal tip subassembly1212 can be securely attached to thecatheter tubing1270 of thecatheter1210 by theproximal adhesive band1244. As further shown inFIG. 6,lumens1276 of thecatheter tubing1270 can be utilized for passage of various elements of thetip subassembly1212 and any of their related features, in addition to instruments, gases, fluids, or other substances.
• A third embodiment of the invention including an alternative distal tip assembly arrangement is shown inFIG. 7. Various details, features and uses of this embodiment include those as described herein regarding other embodiments. In this embodiment an alternative transducer subassembly is provided as shown in detail inFIG. 8. As shown inFIG. 8, theultrasound transducer1320 can be mounted on anangled backing1326. The angle of the backing can range between substantially 0-90°. In one implementation the angle is substantially 10-80o. In another implementation the angle is substantially 30-60°. In another implementation the angle is substantially 40-50°. In a further embodiment the angle is substantially 45°. The transducer can include a shape. In one implementation the transducer is in the shape of an elliptical disc. In another implementation the transducer has a rectangular shape. As shown inFIGS. 7 and 8, in one implementation thetransducer1320 can emit energy in the form of anultrasound beam1358 at an angle to the longitudinal axis of thecatheter1310. As shown inFIG. 7, theultrasound beam1358 can be directed to thetissue146 by appropriately bending thedistal tip assembly1312 using, for example, pull wires as described herein. Theultrasound energy beam1358 can create anablation zone1360 in thetissue146. Cooling of the transducer in this implementation can be achieved as described herein.
• As shown inFIG. 8 theangled backing1326 can be secured in thedistal tip assembly1312 by thedistal adhesive band1318. It is envisioned that other means of securing the backing to the distal tip assembly can include but are not limited to attachment using: adhesive, welding, pins and/or screws or the likes. Still referring toFIG. 8, adistal pull wire1316 can be secured to thedistal tip subassembly1312 by thedistal adhesive band1318. Thedistal pull wire1316 can reside in one of thelumens1376 of thecatheter1310 and can be connected to theslider120 in the proximal housing122 (seeFIG. 1 andFIG. 8). As described above in reference toFIG. 3A, thedistal pull wire1316 can be utilized in bending the distal portion of thecatheter1310. As shown inFIG. 8, thedistal tip subassembly1312 can be securely attached to thecatheter tubing1370 of thecatheter1310 by theproximal adhesive band1344. As further shown inFIG. 8,lumens1376 of thecatheter tubing1370 can be utilized for passage of various elements of thetip subassembly1312 and any of their related features, in addition to instruments, gases, fluids, or other substances.
• A fourth embodiment of the invention including an alternative distal tip assembly arrangement is shown inFIG. 9, and the details of the tip assembly are shown inFIG. 10. Various details, features and uses of this embodiment include those as described herein regarding other embodiments. In this embodiment an alternative transducer subassembly is provided as shown in detailFIG. 10. As shown inFIG. 10, in this implementation, theultrasound transducer1420 is mounted at a distal portion of thedistal tip assembly1412. Further, thetransducer1420 is directed substantially toward the proximal direction. As illustrated, in this orientation thetransducer1420 can emit anultrasound wave1457 substantially parallel to the longitudinal axis of thedistal tip assembly1412.
• As shown inFIG. 10, proximal to thetransducer1420 an angled reflector device can be mounted. For example, the reflector device can be acylindrical reflector1452 with having a face cut at an angle to thedistal tip assembly1412 longitudinal axis. Thereflector1452 can be arranged to reflect theultrasound energy wave1457 produced by thetransducer1420 as anoutgoing ultrasound wave1458 which exits thetubing1442 and travels to the intendedablation site1460 in thetissue146. It is envisioned that the reflector can alternatively include a non-planar face, for example, a curved, convex or concave surface. The angle of the reflector can range between substantially 0-90°. In one implementation the angle is substantially 10-80°. In another implementation the angle is substantially 30-60°. In another implementation the angle is substantially 40-50°. In a further embodiment the angle is substantially 45°.
• Thereflector1452 can be secured to thetubing1442 by means of thedistal adhesive band1418 which can also secure thedistal pull wire1416. Theadhesive band1418 can include apassageway1448 for the flow of a cooling fluid as describe herein. Thetransducer subassembly1414 can be secured at the distal portion of thetip assembly1412 by means of thermally conductive adhesive1450 which, together with theadhesive band1418 forms achamber1446. Thechamber1446 can include one ormore apertures1464. As shown inFIG. 10, in one implementation theapertures1464 are drip holes distributed circumferentially about the distal portion of thedistal tip assembly1412.
• In use, a cooling fluid can be flowed from thepassageway1448 in the distal adhesive band, past thereflector1452 and exit by way of theapertures1464. This fluid flow can serve to cool thetransducer1420 and keep it within nominal operating temperatures. It is envisioned that cooling of the transducer can be controlled to provide nominal transducer operation. As shown inFIG. 10, thetransducer1420 can include atemperature sensor1436, for example, attached to the back side of the transducer. Thetemperature sensor1436 can include associated lead wires, which along with the wires for the transducer can form abundle1440 which is subsequently contained in alumen1476 of thecatheter tube1470. Similarly, thefluid passageway1448 can be in fluid communication with alumen1476 of thecatheter tubing1470. As further shown inFIG. 10, thedistal pull wire1416 can also be contained in alumen1476 of thecatheter tubing1470. As shown inFIG. 10, in oneimplementation tubing1442 is bonded to thecatheter tubing1470 by means ofproximal adhesive band1444.
• Still referring toFIG. 10, adistal pull wire1416 can be secured to thedistal tip subassembly1412 by thedistal adhesive band1418. Thedistal pull wire1416 can reside in one of thelumens1476 of thecatheter1410 and can be connected to theslider120 in the proximal housing122 (seeFIG. 1 andFIG. 10). As described above in reference toFIG. 3A, thedistal pull wire1416 can be utilized in bending the distal portion of thecatheter1410. As shown inFIG. 10, thedistal tip subassembly1412 can be securely attached to thecatheter tubing1470 of thecatheter1410 by theproximal adhesive band1444. As further shown inFIG. 10,lumens1476 of thecatheter tubing1470 can be utilized for passage of various elements of thetip subassembly1412 and any of their related features, in addition to instruments, gases, fluids, or other substances.
• The anchoring mechanism of the device can be configured in any of a number ways in addition to the mechanism as illustrated, for example inFIGS. 3 and 14 wherein a wire loop is included. One function of the anchor mechanism is to provide a firm axis of rotation to the catheter as it is rotated so that the ultrasound beam can be directed to provide a partial or complete zone of ablation. Another function of the anchor mechanism in some implementations is to provide stabilization of the catheter when manipulating the catheter distal portion. As shown inFIG. 14 theanchor mechanism140 can include awire loop138 that can be firmly pressed against the ceiling wall of a heart chamber.
• As shown inFIG. 15, in anotherimplementation anchor mechanism370 including an expandable member, for example, an inflatable balloon is provided. The anchoring member can be in the shape of adisc372 that is inflatable, for example, an inflatable balloon. The shaft of theanchor mechanism370 in this case can be made of asuitable tubing374 for inflating and deflating thedisc372. The disc can be constructed such that when in a deflated profile, the disc can move through an assigned lumen in the catheter (not shown). In use, the device is placed in a heart chamber as described herein. The implementation of theanchor member374 illustrated inFIG. 15 can be advanced beyond thenotch342, and after deployment thedisc372 can be inflated. The inflated disc can be firmly pressed against the ceiling wall of the heart chamber (not shown). Theshaft374 of theanchor mechanism370 in this implementation provides an axis ofcatheter rotation352 around which the distal tip assembly can be rotated to sweep the ultrasound energy beam to create a zone of ablation.Anchor mechanism370 shown inFIG. 15 can be withdrawn into the catheter by deflating the disc and pulling theanchor mechanism370 proximally into the lumen through thenotch342, for example, by actuating a slider mechanism provided at the proximal housing of the catheter.
• Although thedisc372 of thisanchor mechanism370 implementation is described as a balloon (seeFIG. 15), it is envisioned that any type of expandable member could be used. Suitable expandable members can include but are not limited to a cage, stent, or other self-expanding device that can be deployed and collapsed as required. Such structures are well known in the art.
• Another implementation of an anchor mechanism is illustrated inFIG. 16. In this implementation, the distal portion of theanchor mechanism470 includes one ormore barb members472 or similar tissue engaging hooks. As theanchor mechanism470 is deployed by advancing themechanism470 distally beyond thecatheter notch442, thebarb members472 deploy to an open configuration. Upon further advancement of the anchor mechanism, the barb members can engage firmly in the tissue, for example the ceiling wall of the heart chamber (not shown). Again, as shown inFIG. 16, theshaft474 of theanchor mechanism470 provides an axis ofrotation452 for thecatheter410 when thecatheter410 is used for creating a zone of ablation. Thebarb members472 can collapse as theanchor mechanism470 is withdrawn into a lumen of the catheter by way of thenotch442, for example, by actuating a slider mechanism at the proximal housing of the catheter.
• In general, in another aspect, an ablation device including a catheter having a distal tip assembly as described herein, but without a need for physical anchoring to the ceiling wall of the heart chamber is provided. As shown inFIG. 17, in one implementation, theanchor mechanism570 of the ablation device includes adouble wall tubing580 having anannulus582 between aninner wall584 and anouter wall586.Anchor mechanism570 is an elongate structure spanning from a distal portion of the ablation catheter (seeFIG. 17) to substantially the proximal portion of the device (not shown). The distal portion of theanchor mechanism570 includes an expandable member, for example, an inflatable balloon588 (seeFIG. 17) which can communicate with a connector, for example, a luer fitting at the proximal end of the anchor mechanism570 (not shown). Although a balloon is described as an exemplary expandable member, it is envisioned that other expandable members including but not limited to a cage or stent can be used. Theinner lumen590 of theanchor mechanism570 provides a passageway for theablation catheter510 such that the catheter is free to move axially554 and radially552 within. As shown inFIG. 17, during use, theanchor mechanism570 can be positioned inside theguide catheter522 and advanced distally until a distal portion of theanchor mechanism570 extends beyond theguide catheter522 while theballoon588 remains inside theguide catheter522 substantially proximal to theguide catheter522 end. In another implementation at least a part of the expandable member of the anchor mechanism remains inside the guide catheter, while another part of the expandable member extends distally beyond the guide catheter end (not shown). In yet another implementation the distal portion of the anchor mechanism remains substantially proximal to the distal end of the guide catheter (not shown).
• To effect anchoring, the balloon can be inflated with a suitable fluid (e.g., saline or CO₂) sufficiently such that a distal portion of the anchor mechanism is held firmly in the guide catheter. Theablation catheter510 can then be advanced distally (seearrow554 inFIG. 17) through theinner lumen590 of theanchor570. As shown inFIG. 17, when theballoon588 is inflated, the distal portion of thecatheter510 exiting from theanchor mechanism570 is free to rotate in amanner552 about a longitudinal axis, yet is held firmly in theguide catheter522. As required, the catheter distal portion can be shaped by bending as described herein to a desired position (e.g., see FIGS.3A-C). When anchored at the end of the guide catheter, the distal portion of the ablation catheter can be caused to follow a fixed rotational path without being susceptible to wavering or wandering as the catheter is rotated or otherwise guided in the heart chamber to create a zone of ablation.
• The creation of a zone of ablation is facilitated by moving the distal portion of the catheter sufficiently away from the longitudinal axis of the catheter followed by rotation around an axis of rotation provided by an anchor mechanism. The location and orientation of the distal tip assembly, and the resulting direction of the ultrasound energy beam, is determined by the bending of the catheter distal portion at one, two or more locations along the catheter. In one implementation an ultrasound beam is presented to the tissue at a substantially orthogonal angle to achieve efficient ablation of the tissue. The direction of the sound beam can be adjusted by manipulating the bending of the catheter distal portion. This can be achieved by presenting the beam to the tissue in a duty cycle manner where the beam is energized for a pre-determined period followed by a quiet period. During this quiet period, a portion of the sound beam is reflected by the tissue, and the intensity of the reflection is measured by the same transducer being used in a receive mode. An operator or a control system can manipulate the angle of the ultrasound energy beam to maximize the intensity of the reflected sound beam. This ensures that the beam is substantially orthogonal to the tissue. As the beam is swept along the tissue, the distal tip assembly angle can be continuously manipulated such that the beam is presented to the tissue in a substantially orthogonal manner at all times. This can be achieved by a microprocessor controlled system (not shown) which utilizes the information provided by the reflected signal and then manipulates the tip bending through the pull wires connected to appropriate stepping motors. The motor mechanism can be contained in a separate module connected to the generator by means of an electrical cable (not shown). The proximal housing of the ablation catheter can be arranged to engage with the motor module making appropriate connections between the slider mechanisms and the corresponding motors (not shown). The resulting zone of ablation would then achieve maximum ablation, and the irregular anatomy, if any, of the heart chamber would be effectively addressed.
• It is envisioned that a zone of ablation produced using the device described herein can be lesion in tissue having a shape including but not limited to a ring, elliptical, linear, and curvilinear as created by a combination of bending and/or rotating motions of the device.
• In general, in another aspect, methods of using the embodiments described herein, for example, in treating atrial fibrillation, are provided. By way of example, a use of the device of the first embodiment is illustrated inFIG. 11. One method of using the device can include the following steps:
• 1. Aguide catheter sheath222 is positioned across theatrial septum224 of a heart in a conventional way. One such technique is described by Gill (J. S. Gill, How to perform pulmonary vein isolation, Europace 2004 6(2):83-91). The opening of theguide catheter222 is directed towards theceiling226 of the heart chamber.
• 2.Ablation catheter210 is advanced through theguide catheter222 and beyond theguide catheter222 open end towards the tissue area in the middle of the pulmonary veins (PV) such that thedistal tip assembly212 points generally towards a part of the tissue surrounded by the PV.
• 3.Anchor mechanism240 is deployed from within thecatheter210 andwire loop238 is securely positioned against the tissue of theceiling226 of the heart chamber thereby providing an axis of rotation for thecatheter210.
• 4.Tip assembly212 of thecatheter210 is moved away from thewire loop238 by using the bending mechanism described herein and as shown FIGS.3A-C. In general, thedistal pull wire116 is pulled by moving the first slider120 (seeFIG. 1), the catheter distal portion is bent atlocation126 in thedirection172, thereby moving from position X to position Y, as shown inFIG. 3B. Next, theproximal pull wire128, which is secured in the catheter lumen at a position by proximaladhesive band130, is pulled by moving the second slider132 (seeFIG. 1). This results in thecatheter110 distal portion bending atlocation136 and moving in thedirection174 to position Z, away from the longitudinal axis of the catheter, as shownFIG. 3C. In this way a portion or all of thetip assembly212 can be positioned outside an area circumscribing the PV. More specifically, it is envisioned that thetip assembly212 can be positioned suitably, in terms of distance and incident angle (e.g., orthogonal), to ablate tissue outside of an area defined by the PV.
• 5. Thetip assembly212 is oriented towards thetissue226, and the device is energized by a generator (not shown) to provide abeam258 of emitted ultrasound energy which impinges on thetissue226. Thisenergy beam258 creates anablation zone260 in thetissue226.
• 6. The treatment of the tissue is continued until a complete ablation of transmural thickness is achieved.
• 7.Catheter210 is progressively rotated in amanner252 about an axis as indicated inFIG. 11, such that thetip assembly212 and thesound beam258 traverses in a substantially circular path in the heart chamber (indicated as dashedlines262 inFIG. 11). The treatment of tissue along a tissue path is continued until a complete ablation of transmural thickness is achieved along the entire path to create a partial or a complete zone ofablation262 around all the targeted pulmonary veins, thereby achieving a conduction block.
• 8. Theanchor mechanism240 is retracted into a lumen through thenotch242 by actuating the appropriate slider mechanism at the proximal housing (not shown).
• 9.Distal tip assembly212 is returned to a relaxed position by releasing the pull tension on the respective pull wires (not shown) thereby readying thecatheter210 for retraction into theguide catheter222.
• 10. Theablation catheter212 and theguide catheter222 are removed from the body.
• The method outlined above provides for a zone of ablation, having a shape as described herein, around four pulmonary veins. However, as shown inFIG. 12, in another method of using the device a conduction block can be achieved by providing two zones of ablation, for example, ablation rings264 and266, each around two PV. Alternatively, anablation ring268 can be placed around three PV as shown inFIG. 13. It is envisioned that any combination of ablation zones including but not limited to rings could be placed around one, two, three, or four pulmonary veins to achieve a complete conduction block.
• In another implementation a method of using the device described herein can include the following steps:
• 1. Aguide catheter sheath222 is positioned across theatrial septum224 of a heart in a conventional way. The opening of theguide catheter222 is directed towards theceiling226 of the heart chamber.
• 2.Ablation catheter210 is advanced through theguide catheter222 and beyond theguide catheter222 open end towards the tissue area in the middle of the pulmonary veins (PV) such that thedistal tip assembly212 points generally towards a part of the tissue surrounded by the PV.
• 3.Tip assembly212 of thecatheter210 is moved away from thewire loop238 by using the bending mechanism described herein and as shown FIGS.3A-C. In general, thedistal pull wire116 is pulled by moving the first slider120 (seeFIG. 1), the catheter distal portion is bent atlocation126 in thedirection172, thereby moving from position X to position Y, as shown inFIG. 3B. Next, theproximal pull wire128, which is secured in the catheter lumen at a position by proximaladhesive band130, is pulled by moving the second slider132 (seeFIG. 1). This results in thecatheter110 distal portion bending atlocation136 and moving in thedirection174 to position Z, away from the longitudinal axis of the catheter, as shownFIG. 3C. In this way a portion or all of thetip assembly212 can be positioned outside an area circumscribing the PV. More specifically, it is envisioned that thetip assembly212 can be positioned suitably, in terms of distance and incident angle (e.g., orthogonal), to ablate tissue outside of an area defined by the PV.
• 4.Anchor mechanism240 is deployed from within thecatheter210 andwire loop238 is securely positioned against the tissue of theceiling226 of the heart chamber thereby providing an axis of rotation for thecatheter210.
• 5. The device is energized by a generator (not shown) to provide abeam258 of emitted ultrasound energy which impinges on thetissue226. Thisenergy beam258 creates anablation zone260 in thetissue226.
• 6. The treatment of the tissue is continued until a complete ablation of transmural thickness is achieved.
• 7.Catheter210 is progressively rotated in amanner252 about an axis as indicated inFIG. 11, such that thetip assembly212 and thesound beam258 traverses in a substantially circular path in the heart chamber (indicated as dashedlines262 inFIG. 11). The treatment of tissue along a tissue path is continued until a partial or a complete zone of ablation of transmural thickness is achieved along the entire path to create complete ablation, for example, shaped as aring262 around all the targeted pulmonary veins, thereby achieving a conduction block.
• 8. Theanchor mechanism240 is retracted into a lumen through thenotch242 by actuating the appropriate slider mechanism at the proximal housing (not shown).
• 9.Distal tip assembly212 is returned to a relaxed position by releasing the pull tension on the respective pull wires (not shown) thereby readying thecatheter210 for retraction into theguide catheter222.
• 10. Theablation catheter212 and theguide catheter222 are removed from the body.
• In a further implementation, wherein the anchor mechanism of the device is the mechanism as shown inFIG. 17 and as described herein, a method of using the device can include the following steps:
• 1. Referring to generally toFIG. 11 (disregarding theanchor mechanism240 depicted therein), aguide catheter sheath222 is positioned across theatrial septum224 of a heart in a conventional way. The opening of theguide catheter222 is directed towards theceiling226 of the heart chamber.
• 2. Referring now toFIG. 17,anchor mechanism570 is advanced through theguide catheter522 and beyond theguide catheter522 open end towards the tissue area in the middle of the pulmonary veins (PV) (not shown) such that theanchor mechanism522 points generally towards a part of the tissue surrounded by the PV.
• 3. Referring still toFIG. 17, theballoon588 of theanchor mechanism570 is inflated with a fluid such that a distal portion of theanchor mechanism570 is held firmly in theguide catheter522.
• 4. Theablation catheter510 is advanced through theinner lumen590 of theanchor mechanism570 and into the heart chamber.
• 5. Referring generally again toFIG. 11 (disregarding theanchor mechanism240 depicted therein), thetip assembly212 of thecatheter210 is bent into a shape using the bending mechanism described herein and as shown FIGS.3A-C. Thus, a portion or all of thetip assembly212 is positioned outside of an area circumscribing the PV.
• 6. The device is energized by a generator (not shown) to provide abeam258 of emitted ultrasound energy which impinges on thetissue226. Thisenergy beam258 creates anablation zone260 in thetissue226.
• 7. The treatment of the tissue is continued until a complete ablation of transmural thickness is achieved.
• 8. Referring again toFIG. 17,catheter510 is progressively rotated about an axis in amanner552 such that the tip assembly and the sound beam traverses in a substantially circular path in the heart chamber (indicated as dashedlines262 inFIG. 11). The treatment of tissue along a tissue path is continued until a partial or a complete ablation of transmural thickness is achieved along the entire path. Thus, acomplete ablation ring262 is made around all the targeted pulmonary veins, thereby achieving a conduction block.
• 9. The catheter512 is returned to a relaxed position by releasing the pull tension on the respective pull wires (not shown) and thecatheter510 is retracted through the anchor mechanism.
• 10. Theballoon588 of theanchor mechanism570 is deflated and theanchor mechanism570 is retracted through theguide catheter522 and theguide catheter522 is removed from the body.
• In another implementation, the methods described herein can be used to treat the left atrial appendage of the heart. In this case, the method can include use of the ablation device as described herein to produce a conduction block circumscribing the atrial appendage. It is envisioned that the atrial appendage can be treated alone or in conjunction with treatment of the PV using the ablation device of the invention.
• Referring to the embodiment ofFIG. 18, the system consists of acatheter set100, twopositioning wires2128 and2130, and aguide sheath2118. The catheter set100 is composed of two catheters, atherapy catheter2110 which is slideably contained in anouter catheter2112.Catheter2110 consists of ahousing2114 which contains theultrasound transducer2116. A more detailed description of thehousing2114 is presented later in this specification.Catheter2110 is contained in theouter catheter2112. Thecatheter2112 is further contained in thetransseptal guiding tube2118.Catheter2112 has three independent movements available. First, thecatheter2112 can move axially in theguide tube2118 as depicted by2120. The distal tip of thecatheter2112 is equipped to be bent in amanner2122. Finally, thecatheter2112 can be rotated in theguide sheath2118 in amanner2124.Catheter2112 contains alumen2126 which houses the locatingwire springs2128 and2130.Wires2128 and2130 are independently movable in thelumen2126 ofcatheter2112.
• The elements of the catheter systems are positioned in the left atrium (LA) of the heart. Thewires2128 and2130 are positioned in the left pulmonary veins (LPV). Thetherapy catheter2110,outer catheter2112, and the distal portion of theguide sheath2118 are positioned in the chamber of the left atrium. Other structures of the heart shown inFIG. 18 are the mitral valve opening (MV), left atrial appendage (LAA), and right pulmonary veins (RPV).
• At the proximal end, the various catheter elements are connected to a variety of controls in aconnector console2132. After placement in the septum of the heart, theguide sheath2118 is locked in position by means of thelever2134. The locatingwires2128 and2130 havemarkers129 and131 respectively at their proximal ends. The locatingwires2128 and2130 are designed to be guided by hand by the surgeon, and after the intended positioning, are locked in by means of thelever mechanisms2136 and2138 at the position of themarkers129 and131. Thelinear movement2120 of theouter catheter2112 is achieved by moving theslider2140 which moves linearly inslot2142. Once the desired position of thecatheter2112 is achieved, theslider2140 can be locked in position. Therotational movement2124 of theouter catheter2112 is achieved by thegear mechanism2144 and2146.Gear2144 is attached to the proximal end of theouter catheter2112.Gear2144 is driven by thepinion2146 which is attached to a motor (not shown). Thebending mechanism2122 of the distal tip of thecatheter2112 is achieved by means of thepull wire2148 which terminates in aslider mechanism2150 which is lockable once the desired position of the bending of thecatheter2112 is achieved. All the motions described here can be achieved by hand or by using appropriate motors, linkages, and actuators in theconsole2132.
• Similar to theouter catheter2112, thecatheter2110 also is provided with three independent movements. First, thecatheter2110 can be moved axially in thecatheter2112 as shown bymovement2152. Thismovement2152 is controlled at the proximal end by means of theslider2158 which is lockable once the desired position of thetherapy catheter2110 is achieved in theouter catheter2112. Second, the distal portion of thecatheter2110 can be bent in themanner2124 by means of a pull wire (not shown) connected to theslider mechanism2160 at theproximal end console2132. Again, theslider2160 is lockable in position once the desired position of the bend of the tip of thecatheter2110 is achieved. Finally, thecatheter2110 can be rotated in theouter catheter2112 in a manner shown as2156. This motion is effected by thegear mechanism2162 and2164 in theconsole2132.Gear2162 is attached to the proximal end of thecatheter2110, and it is driven by thepinion2164 which is connected to a motor (not shown). Thecatheters2110 and2112 contain the corresponding orientation marks2166 and2168 provided on the shafts thereof. The console also consists of aconnector2170 which electrically connects to a power generator and controller (not shown). Theconnector2170 also provides electrical connections to thepositioning wires2128 and2130 by means of being connected to the locking levers2136 and2138 in theconsole2132. As described later, theconnector2170 provides electrical connections to theultrasound transducer2116, a temperature sensor at thehousing2114, and thepositioning wires2128 and2130.
• FIG. 36 shows the positions of the catheter elements in the left atrium. The locatingwires2128 and2130 are positioned in the two pulmonary veins (LPV1 and LPV2). As shown in the figure, thehousing2114 at the tip of thecatheter2110 points towards thewall tissue2174 of the atrium. As described in detail later, theultrasound element2116 in thehousing2114 emits an ultrasound beam to establish anablation window2172. Now, as theouter catheter2112 is rotated inside theguide sheath2118 in themanner2124 and around the locatingwires2128 and2130, theultrasound beam2172 sweeps a generallycircular path2176 creating a section of a conical shell. The purpose of the twopositioning wires2128 and2130 is to assure that the rotation of thehousing2114 will occur in a path outside the pulmonary vein LPV1 and LPV2. The objective of the invention is to find at least one such curve where thesweep path2176 of theultrasound beam2172 intersects with theatrial wall tissue2172 in a contiguous locus.
• FIG. 20 shows the catheter apparatus. Thetherapy catheter2110 and theouter catheter2112 form aconjoined set100 which can be freely moved axially in theguide sheath2118. Thevery tip section186 of thesheath2118 has a snug fit over theouter catheter2112 so as to provide a firm grip on thecatheter2112 while it is performing itsrotation2124.Catheter2112 can also be moved axially inside theguide sheath2118 in amanner2120. In addition, the tip of thecatheter2112 can be bent about apivot point182 in amanner2122.Catheter2112 has aseparate lumen2126 which houses the locatingwires2128 and2130. These wires exit at thenotch127 and can be advanced or retracted in amanner178 and180. Thewires2128 and2130 are constructed from a material such as nitinol so as to take the shape ofconical springs194 and196 respectively when in free space. The ends of the positioning wires can also be shaped in a suitable configuration other than the conical shapes described herein. Thetips190 and192 of thewires2128 and2130 are made of a soft spring coil so as not to cause any injury to the tissue of the heart where the tips might be in contact and move against. Thewires2128 and2130 can be advanced in the atrial chamber with the intention of being positioned in the two pulmonary veins. Thewires2128 and2130, when residing completely inside thelumen2126 of thecatheter2112, are held in a generally straight shape conforming to confines of the lumen2126 (ref.FIG. 23). As they are advanced outwards, and as they exit thenotch127, they take on the predetermined shape ofconical springs194 and196. Therotation2124 of thecatheter2112 is essentially around thewires2128 and2130 withlumen2126 serving as the axis of said rotation.
• As described earlier, thetherapy catheter2110 similarly has three degrees of motion. It can move axially in theouter catheter2112 in amanner2152.Catheter2110 can be bent in amanner2154 around apivot point184. Finally, thecatheter2110 can be rotated in themanner2156. Thetip end188 of theouter catheter2112 has a snug fit over thecatheter2110 to provide a firm support during therotation2156 of thecatheter2110. Otherwise, thecatheter2110 is freely movable inside theouter catheter2112 in amanner2152.
• The tip of thecatheter2110 has ahousing2114 which contains anultrasound transducer2116.FIG. 21A shows the details of thehousing2114. Thetransducer2116, which is of a generally circular shaped disc fabricated from a suitable piezoelectric material, is bonded to the end of acylindrical backing198 by means of anadhesive ring200. The attachment of thetransducer2116 to thebacking198 is such that there is anair pocket202 between the back surface of thetransducer2116 and thebacking198. Thisair pocket202 is useful in the sense that when thetransducer2116 is energized by the application of electrical energy, the emitted ultrasound beam is reflected by theair pocket202 and directed outwards from thetransducer2116. Theair pocket202 can be replaced by any other suitable material such that a substantial portion of the ultrasound beam is directed outwards from thetransducer2116. Backing198 can be made of a metal or a plastic, as shown in more detail inFIG. 21B, such that it provides a heat sink for thetransducer2116. Thecylindrical backing198 has a series ofgrooves204 disposed longitudinally along the outside cylindrical wall. The purpose of the grooved backing is to provide for the flow of a cooling fluid2224 substantially along the outer surface ofbacking198 and past the face of thetransducer2116. The resulting fluid flow lines are depicted as206 inFIG. 21A. In an actual clinical situation, saline or any other physiologically compatible fluid can be used as the cooling fluid2224 at any safe temperature preferably below the body temperature of 37° Celsius.
• Thetransducer2116 has anelectrical contact208 on the front surface of the transducer using a suitablyinsulated wire214. Theelectrical contact208 can be made by standard bonding techniques such as soldering or wire bonding. Thecontact208 is preferably placed closer to the edge of thetransducer2116 so as not to disturb theultrasound beam2226 emitted by thetransducer2116 upon being electrically energized. The front face of thetransducer2116 is covered with another material known as thematching layer228. The purpose of thematching layer228 is to increase the efficiency of coupling of theultrasound wave2226 into the surroundingfluid2224. Generally, as the ultrasound energy moves from thetransducer2116 into thefluid2224, the acoustic impedances are different in the two media, resulting in a reflection of some of the ultrasound energy back into thetransducer2116. Amatching layer228 provides a path of intermediate impedance so that the sound reflection is minimized, and the output sound from thetransducer2116 into thefluid2224 is maximized. The thickness of thematching layer228 is maintained at one quarter of the wavelength of the sound wave in the matching layer material. There are a number of material candidates, generally from a family of plastics, which can serve as the matching layer. One such material is parylene which can be easily placed on the transducer face by a vapor deposition technique. In addition one can deposit a multitude of matching layers, generally two or three, on the face of the transducer to achieve maximum energy transmission from thetransducer2116 into thefluid2224. Conversely, same reflection principle is used on the backside of thetransducer2116. Here theair pocket202 is provided. Ultrasound energy sees a large impedance mismatch, so a majority of energy is reflected back into thetransducer2116 and emitted from its front face. Thus by using a combination of theair pocket202 on the back and matching layer(s)228 on the front, the efficiency of thetransducer2116 is greatly enhanced. Alternatively, theair pocket202 could be replaced with a backing block material that minimizes reflections from the behind thetransducer2116. While this backing block can reduce the amount of energy transmitted from the front oftransducer2116, it removes reverberations and other artifacts whentransducer2116 is operating as an ultrasound receiver. The backing block material is designed to maximize the efficiency oftransducer2116 while providing adequate suppression of imaging artifacts.
• The back side of thetransducer2116 also has anelectrical connection2210 to a suitablyinsulated wire216. Again, the bonding can be done in any of the conventional manner such as a solder joint or wire bonding.Wires214 and216 together form apair218 which can be a twisted pair or miniature coaxial cable. On the backside of thetransducer2116, there istemperature sensor2212. Its purpose is to monitor the temperature of thetransducer2116 during its use. The sensor can be a thermocouple or a thermistor of appropriate size so as to cover a small portion of the transducer surface. Twowires220 provide the electrical connection to thetemperature sensor2212. The wire pairs218 and220 form abundle2222. The flow of the cooling fluid is achieved through alumen2242 which is terminated in afluid port254 at the proximal end (ref.FIG. 18).
• The transducer—backing subassembly is encased in atubular jacket230. The material of the jacket can be metal or plastic. The tubular jacket protrudes distally beyond thetransducer2116 to form a fluid chamber orpocket236. Thispocket236 provides for a column of fluid2224 which is in a physical and thermal contact with thetransducer2116. This invention provides for thefluid column2224 for two distinct objectives. First, thecolumn2224 provides for the thermal cooling of theultrasound transducer2116. Thiscolumn2224 is at a lower temperature than the transducer face and therefore aids in cooling thetransducer2116. The temperature of the fluid2224 can be easily controlled by providing the cooling fluid at a suitable temperature. The temperature of the transducer is constantly monitored by thetemperature sensor2212 disposed on the back of thetransducer2116. Secondly, the fluid column provides for a separation medium between theultrasound transducer2116 and the blood surrounding thehousing2114 during the use of the device in a clinical setting.
• Still referring toFIG. 21A, thetubular jacket230 is shown at its distal end in a “castle head” configuration withslots239. The purpose of theslots239 is to provide for exit ports for the flowingfluid2224. Theslots239 are desirable for the situation when the front tip of the catheter is in contact with the tissue or other structures during the use of the device, to maintain the important flow of the cooling fluid. Thefluid flow lines206 flow along thegrooves204, bathe thetransducer2116, form thefluid column236 and exit through theslots239 at thecastle head2238. The maintenance of the fluid flow through thetubular jacket230 can be achieved in a number of different ways. One additional such way is shown inFIG. 21C where thetubular jacket230 consists of an enclosed chamber withsmall holes2240 on the cylindrical surface closer to the distal end. Theseholes2240 provide for the exit path for the flowing fluid.
• It is important to maintain the transducer functioning at a lower temperature so as to operate at a safe temperature for the patient, and to preserve consistent performance of the piezoelectric material, which can be damaged by exposure to excessive heat.
• Another important function of the housing design of this invention is to provide a barrier between the face of thetransducer2116 and the blood residing in the atrium of the heart. If the fluid flow is not incorporated, and the transducer face is directly in contact with blood, the blood will coagulate on the surface of thetransducer2116. The coagulation will be further aggravated if the transducer gets hotter during its operation. The coagulated blood will provide a barrier to transmission of the ultrasound energy in an unpredictable way depending on the coverage of the transducer face by the coagulated blood. Additionally, there is serious risk of forming a blood clot at the interface of thetransducer2116 and the surrounding blood. The incidence of any blood clot is undesirable in any situation in the heart chamber. The flow of the cooling fluid, as described in this invention, keeps the blood from getting in contact with the transducer face, thus avoiding the formation of blood clots. We have determined that a flow rate of approximately 1 ml per minute is sufficient to maintain thefluid column236 and keep the separation between the blood and the face of the transducer.
• FIG. 21A shows the mounting of thetransducer2116 at an angle of 90 degrees to the axis of thecatheter housing2114. However, thetransducer2116 can also be mounted at any other angle. The exit path of the beam will be at 90 degrees to the face of the transducer. The remaining details of the catheter and the presentation of the ultrasound beam to the tissue will vary accordingly in order to achieve the intended effect of tissue ablation.
• Thetransducer disc2116, as shown inFIG. 21A, has a flat front surface. This front surface of the transducer can be either concave or convex to achieve an effect of a lens.
• Thetubular jacket230 of the above description is attached to acatheter tubing234 by means of adhesive232. Apull wire248 also is secured in the adhesive232. Thepull wire248 is contained in alumen244. Thispull wire248 is utilized in bending the tip of thecatheter2110 in a manner2154 (ref.FIG. 18). Anotherlumen2242 provides the path for the fluid flow. Thewire bundle2222 is contained in a yetseparate lumen246 in thecatheter tube234.
• Referring toFIG. 22 showing the cut-away section, thecatheter tubing234 constitutes of a multilumeninner tubing235 covered with abraid250 and ajacket2252. Themultilumen tubing235 has three lumens. Thelumen2242 is terminated in a fluid port254 (ref.FIG. 18) at the proximal end of thecatheter2110. This allows the cooling fluid to be passed through the length the catheter and exit at the ‘castle head’2238 ofhousing2114. Thelumen246 contains thewire bundle2222, and thelumen244 contains thepull wire248. Thetubing2240 is encased in abraid250 in a conventional way. The material of the braid can be round or flat metal wires, plastic filaments, or Kevlar. It is understood that the braid can be replaced with a spring like wrapping or a wrapping of foil. Finally, thebraid250 is covered in asmooth jacket2252. The material of the jacket is generally plastic, and can be placed using conventional extrusion techniques. Thebraid250 and thejacket2252 together provide the tortional control of thecatheter tubing234. The tortional control is required to achieve the rotation2156 (ref.FIG. 18) of thetherapy catheter2110.
• Next, the construction of theouter catheter2112 is shown in a cut-away section inFIG. 23. Thecatheter tubing256 consists of a multilumen tubing257 which is encased in abraid2268 and ajacket270. Themultilumen tubing256 has three lumens, onelumen2258 contains a pull wire2260 which is terminated at the tip in anadhesive band2262. This pull wire is utilized in bending the outer catheter tubing in the manner2122 (ref.FIG. 18). Anotherlumen2126 is provided for thepositioning wires2128 and2130. Themultilumen tubing256 is encased in abraid2268 in a conventional way. The material of the braid can be round or flat metal wires, plastic filaments, or Kevlar. It is understood that the braid can be replaced with a spring like wrapping or a wrapping of foil. Finally, thebraid2268 is covered in asmooth jacket270. The material of the jacket is generally plastic, and can be placed using conventional extrusion techniques. Thebraid2268 and thejacket270 together provide the tortional control of theouter catheter tubing2112. The tortional control is required to achieve the rotation2124 (ref.FIG. 18) of theouter catheter2112.
• When energized with an electrical pulse or pulse train, the transducer emits a sound wave with properties determined by the characteristics of thetransducer2116, thematching layer228, thebacking202, the electrical pulse, and the tissue in front of the transducer. These elements determine the frequency, bandwidth and amplitude of the sound wave propagated into the tissue. Typically, the frequencies of the emitted sound are in the low megahertz range. For the intended use in this invention, for tissue imaging and ablation near the transducer, the useful frequencies range from 5 to 25 megahertz.
• During one of the actual uses of the device of this invention, it will be placed in the atrium of the heart. Referring toFIG. 24, thetransducer2116 is maintained separated from the surroundingblood284 by afluid column236. When thetransducer2116 is energized with an appropriate electrical pulse, it emits abeam272 of ultrasound energy. A typical beam pattern is shown for the ultrasound wave as it is emitted by thetransducer2116. This beam pattern illustrates the outline of the ultrasound beam by mapping where the sound pressure falls by 6 dB relative to the midline of the beam. Thesound beam272 travels in thedirection274 away from thetransducer2116 in a generally collimated manner up to a distance of L and then diverges thereafter. The diameter at the origin of theultrasound beam272 corresponds to the diameter D of thetransducer disc2116. If the device relies on the natural focusing of a flat disc transducer, theultrasound beam272 converges slightly up to a depth of L, beyond which the beam diverges. The minimum beamwidth D′ occurs at the distance L. It is well known that the distance L is determined by the diameter of the transducer disc D and the operating frequency. These relationships are well summarized by Bushberg et al [The Essential Physics of Medical Imaging,2nd edition, Bushberg, Seibert, Leidholdt and Boone, Lippincott Williams & Wilkins, 2002; p. 491]. In this invention, a relatively large L is desired, since it establishes the size of theablation window2172. A variety of disc diameters and operating frequencies can be used. In general, D is selected as large as possible for a given device diameter, so that L is maximized. A higher operating frequency will also increase the distance L. However since ultrasound is attenuated in tissue as a function of increasing frequency, the required depth of the lesions determines the useable maximum frequency. Given the constraints of device size and ultrasound attenuation, this invention uses, for example, an operating frequency of 12 MHz and a disc diameter of 2.5 mm, resulting in a depth L of 12 mm and a minimum beamwidth D′ of 1.6 mm.
• The natural focusing of a flat disc transducer provides adequate beam forming for typical uses of this invention. Adding an acoustic lens in front oftransducer2116 provides additional flexibility in adjusting the beam pattern. For example, an acoustic lens could create a beam that is more uniformly collimated, such that the minimum beamwidth D′ approaches the diameter of the disc D. This will provide a more uniform energy density in theablation window2172, and therefore more uniform lesions as the tissue depth varies within the window. A lens could also be used to move the position of the minimum beamwidth D′, for those applications that may need either shallower or deeper lesion. This lens could be fabricated from plastic or other material with the appropriate acoustic properties, and bonded to the face oftransducer2166. Alternatively, the circular piezoelectric disc could be fabricated with a front face that is curved instead of flat. A slight concave shape, for example, would move the focal point (i.e. smallest D′) in towards the transducer, while a slight convex shape would move the focus outwards.
• The interaction of the ultrasound beam with the tissue is shown inFIG. 25. Thetissue276 is presented to theultrasound beam272 within the collimated length L. Thefront surface280 of thetissue276 is at a distance d (282) away from the face of thecastle head2238. As theultrasound beam272 travels through thetissue276, its energy is absorbed by thetissue276 and converted to thermal energy. This thermal energy heats the tissue to temperatures higher than the surrounding tissue. The result is aheated zone278 which has a typical shape of an elongated tear drop. The diameter D1 of thezone278 is smaller than the beam diameter D at thetissue surface280. This is due to the thermal cooling provided by the surrounding fluid (cooling fluid286 or blood284) which is flowing past thetissue surface280. As the ultrasound beam travels deeper into the tissue, the thermal cooling is provided by the surrounding tissue, which is not as efficient as that on the surface. The result is that theablation zone278 has a larger diameter D2 than D1 as determined by the heat transfer characteristics of the surrounding tissue as well as the continued input of the ultrasound energy from thebeam272. During this ultrasound-tissue interaction, the ultrasound energy is being absorbed by the tissue, and less of it is available to travel further into the tissue. Thus a correspondingly smaller diameter heated zone is developed in the tissue, and the overall result is the formation of theheated ablation zone278 which is in the shape of an elongated tear duct limited to adepth288 into the tissue.
• The interaction of ultrasound energy with the live tissue is well studied and understood. One such description is presented in the article by Gail ter Haar “Acoustic Surgery, Physics Today, December 2001”. In thezone278 where the tissue is heated, the tissue cells are rendered dead due to heat. The temperatures of the tissue typically are above 55° Celsius in theheated zone278 and the tissue is said to be ablated. Hence, thezone278 can be depicted as the ablation zone.
• Referring toFIG. 25, it is important to present thetissue276 to theultrasound beam272 such that the tissue is within the collimated length L to achieve effective ablation. As thebeam272 is presented to the tissue for an extended period of time, theablation zone278 extends into the tissue, but not indefinitely. There is a natural limit of the depth of theablation zone278 as determined by the factors such as the attenuation of the ultrasound energy, heat transfer provided by the healthy surrounding tissue, and the divergence of the beam beyond the collimated length L. This effect is beneficial in the sense that there is a natural safety limit to the penetration of the ultrasound energy such that theablation zone278 stops growing as a steady state is reached between the input of ultrasound energy and its conversion in to thermal energy which is dissipated by the surrounding tissue.
• The ablation zone in the tissue is formed by the conversion of the ultrasound energy to thermal energy in the tissue. The formation of the ablation zone is dependent on time as shown in FIGS.26 A-D, which show the formation of the lesion at times t1, t2, t3 and t4, respectively. As thesound beam272 initially impinges on thefront surface280 of thetissue276 at time t1, heat is created which begins to form the lesion278 (FIG. 26A). As time passes on to t2, and t3 (FIGS. 26B and 26C, theablation zone278 continues to grow in diameter and depth. This time sequence from t1 to t3 takes as little as 3 to 5 seconds, depending on the ultrasound energy density. As the incidence of the ultrasound beam is continued beyond time t3, theablation lesion278 grows slightly in diameter and length, and then stops growing due to the steady state achieved in the energy transfer from its ultrasound form to the thermal form. The example shown in ofFIG. 26D shows the lesion after an exposure t4 of approximately 30 seconds to theultrasound beam272. Thus the lesion reaches a natural limit in size and does not grow indefinitely.
• The ultrasound energy density determines the speed at which the ablation occurs. The acoustic power delivered by the transducer divided by the cross sectional area of the beamwidth determines the energy density per unit time. In this invention, effective acoustic power ranges from 0.3 watt to >10 watts, and the corresponding energy densities range from 3 watts/cm²to >100 watts/cm². These energy densities are developed in the ablation zone. As the beam diverges beyond the ablation zone, the energy density falls such that ablation will not occur, regardless of the time exposure.
• One aspect of this invention is to provide a device which will produce an ablation zone across the entire thickness of the wall of the atrial tissue in order to completely block the conduction of abnormal electrical impulses. This is termed as a transmural lesion. The transmural lesion279, as shown inFIG. 26C, is formed when the entire thickness of thetissue276 is in theablation window2172, and sufficient time is allowed for the lesion to develop.
• The dependence of the formation of theablation zone278 on thegap distance282 between the catheter tip and the tissue surface is shown in FIGS.27A-D. For a uniformly collimated beam, as thegap distance282 increases, thedepth288 of theablation zone278 remains constant. Even for cases where the beam is not uniformly collimated, as in the case of this invention where the beam convergences slightly over distance L, thedepth288 of theablation zone278 varies little as long as the tissue resides in an approximately collimated zone L. This distance L where theultrasound beam272 is approximately collimated, and where an ablation zone is effectively created, is termed as theablation window2172. Thereafter thedepth288 decreases dramatically mainly due to the divergence of theultrasound beam272.
• In practice, the amount of beam convergence can be varied to partially compensate for tissue attenuation, thereby creating more uniform energy densities within the ablation window. This compensation helps reduce the variations indepth288 of theablation zone278 for tissues falling in theablation window2172.
• There is another important factor contributing touniform ablation depths288 within theablation window2172 independent of thegap distance282. The sound beam travels through the cooling fluid and blood in thegap282 with very little attenuation. Therefore almost the entire acoustic energy is available and presented to thetissue276 beginning at the front surface of thetissue280.
• For the practical use of the device of this invention, the discussion of some of the important parameters is presented. Above, we discussed thegap distance282. Thegap distance282 is the distance between the distal end of thecastle head2238 and thefront surface280 of thetissue276. Now we discuss the angle of incidence as shown inFIGS. 28A and 28B. Thetissue276 is presented to theultrasound beam272 such that itsfront face280 is at an angles θ1 and θ2 to thebeam272 at agap distance282. The resultingablation278 is formed in the tissue in the line of thedirection274 of the beam travel. The formation of thezone278 is somewhat independent of the angle of incidence θ. Again, as long as thetissue278 is presented to theultrasound beam272 within theablation window2172, the resultingablation zone278 profiles will be generally similar in shape, size, and depth and somewhat independent of the incidence angle θ.
• In the actual clinical setting, the wall of the atrial tissue is moving within some physical distances. In order to achieve a contiguous transmural lesion in the moving wall of the atrium, the entire movement must be within theablation window2172. As shown inFIG. 29, theatrial wall tissue276 is moving over a distance of R within theablation window2172. So long as the movement R is within theablation window2172, an effectivetransmural lesion278 will be created. Therefore it is important to position thecastle head2238 close enough to the endocardial surface of the atrial wall to ensure a transmural lesion in a moving wall.
• One aspect of this invention is to present the ultrasound beam to the atrial tissue and move it across the tissue such that a contiguous ablation zone (lesion) is created in the tissue wall. Referring toFIG. 19, thezone2172 depicts the cylindrical region in front of thetransducer2116 where theatrial wall tissue2174 is effectively ablated. As thecatheter2112 is rotated in themanner2124, thezone2172 sweeps in a circle creating asection2176 of a cone. Thecatheter housing2114 can also be moved inside the atrium in geometry other than a circle by utilizing the various other movements available for thecatheters2110 and2112. Thus the sweeping ultrasound beam will form acomplex pattern2176 inside the atrium. Theatrial wall tissue2174 intersects thispattern2176 forming a somewhat complex shaped lesion of ablated tissue. The important requirement for effective therapy is to create a contiguous transmural lesion which will serve as a conduction block in stopping the aberrant electrical pathways in the atrium which cause the fibrillation of atrial tissue.
• Referring toFIG. 18, theultrasound transducer2116 is connected to an electrical generator (not shown) by means of theconnector2170 which contains thewires214 and216 connected to the two faces of thetransducer2116. When energized by the generator (not shown), thetransducer2116 emits ultrasound energy at a frequency in the range of 1 to 20 megaHertz (MHz). A practical range of frequency is 5 to 15 MHz. It is well understood in physics of ultrasound, as the frequency increases, the depth of penetration of ultrasound energy in to the tissue is reduced resulting in an ablation zone276 (ref.FIG. 25) ofshallower depth288. The energy of theultrasound beam272 is determined by the excitation voltage applied to the transducer. The generator provides the appropriate frequency and voltage to the transducer to create the desiredsound beam272. For the purpose of the description of this invention, we are using a frequency in the range of 5 to 15 MHz, and a voltage in the range of 10 to 100 volts peak-to-peak. In addition, a variable duty cycle can be used to control the average power delivered to the transducer. The duty cycle ranges from 0% to 100%, with a repetition frequency of approximately 40 kHz, faster than the time constant of thermal conduction in the tissue. This results in anablation zone278 which is created within 2 to 5 seconds, and is ofdepth288 of approximately 5 millimeters (mm), and of a maximum diameter of approximately 2.5 mm in correspondence to the diameter of thetransducer2116. It is understood that the ultrasound transducer of different diameters and frequencies can be used and different voltages and duty cycles can be applied to get various outputs of ultrasound power resulting in differentsized ablation zones278.
• A contiguous transmural lesion is intended as theultrasound beam272 is swept across the atrial wall. Therefore, it would be desirable to know if a contiguous transmural lesion is indeed being created as the ultrasound beam is moved across the moving atrial wall. This is achieved by using thesame ultrasound transducer2116 in a diagnostic mode as described below.
• The effectiveness of the creation of a transmural lesion279 is in knowing and ensuring that theatrial wall tissue2174 is being presented to the ultrasound beam with thepattern2176 for effective ablation (ref.FIG. 19). This is achieved by using thesame ultrasound transducer2116 for the purpose of tissue detection. On the one hand, in order to achieve ablation (i.e. killing of the live tissue cells), the ultrasound beam of sufficient energy is delivered to the tissue in a substantially continuous manner such that the energy input exceeds the thermal relaxation provided by the cooling due to the surrounding tissue. This mode of energizing theultrasound transducer2116 is termed as the ablation mode. On the other hand, the tissue detection is done by utilizing a pulse of ultrasound of short duration which is generally not sufficient for heating of the tissue. Ultrasound has been traditionally used for diagnostic purposes for a number of years. Typical uses are fetal ultrasound imaging, intravascular ultrasound imaging, and the like. For the purpose of this invention, we use the ultrasound to detect the gap (namely, the distance of the tissue surface from the castle head), the thickness of the tissue targeted for ablation, and the characteristics of the ablated tissue. This mode of energizing thetransducer2116 is termed as the diagnostic mode. One objective of this invention is to utilize the diagnostic mode in guiding the therapy provided by the ablation of the tissue.
• This invention uses a simple ultrasound imaging technique, referred to in the art as A Mode, or Amplitude Mode imaging. A short electrical pulse or train of pulses excites the ultrasound transducer creating a short duration ultrasound pulse wave that propagates into the blood and tissue. As the ultrasound pulse travels through the tissue, some of the acoustic energy is backscattered to the transducer, which converts the returning acoustic signal into an electrical voltage. The amplitude of the voltage is sensed in a receiver (not shown), as a function of the time elapsed from the initial transmitted pulse. Since ultrasound travels through blood and soft tissue at a known and approximately constant speed, the receiver can determine the distance from which the returning signals originate. The amplitude of the returning signals depends on the acoustic properties of the tissue. Homogeneous tissue backscatters the sound as the pulse wave propagates through it. Different tissues create differing amounts of backscatter, so the returning ultrasound signal has different amplitudes depending on the type of tissue. As the pulse travels passes from one tissue to another, a reflection occurs, the amplitude of which is determined by the acoustic impedance difference of the two tissues.
• Referring toFIG. 30, thetransducer2116 sends apulse290 of ultrasound towards thetissue276. A portion of the beam is reflected and backscattered as292 from thefront surface280 of thetissue276. This reflectedbeam292 is detected by the transducer2116 a short time later and converted to an electrical signal which is sent to the electrical receiver (not shown). The reflectedbeam292 is delayed by the amount of time it takes for the sound to travel from thetransducer2116 to thefront boundary280 of thetissue276 and back to thetransducer2116 now serving as an ultrasound detector. This travel time represents a delay in receiving the electrical signal from thetransducer2116. Based on the speed of sound in the intervening media (saline fluid286 and blood284), the gap distance d (282) can be determined. As the sound beam travels further into thetissue276, aportion294 of it is reflected from the back surface and travels towards the transducer. Again, the transducer converts this sound energy into electrical signals and the generator converts this information into the thickness t (300) of thetissue276 at the point of the incidence of theultrasound pulse290. As thecatheter housing2114 is traversed in amanner301 across thetissue276, the ultrasound transducer continuously detects the gap distance d (282) and the tissue thickness t (300). This information is used in delivering continuous ablation of thetissue276 during therapy as discussed below.
• The returning echo from tissue boundaries has the same time duration as the transmitted pulse. The returning backscattered signal from the bulk of the tissue has a time duration equal to the path length of the pulse through the tissue. The returning signal fromtissue276 then is a composite of two short relatively high amplitude pulses returning from thefront wall280 andback wall298, along with the backscatter from within the tissue. The amplitude of the backscatter from the tissue will change as the pulse traverses the ablated tissue and the normal tissue. Therefore, by measuring the relative amplitudes of the returning signal, the receiver can determine the depth of the front wall, the depth of the lesion, residual tissue depth that is not yet ablated, and the depth of the back wall.
• The receiver compares the time delay of the first echo from the face oftissue280 to a time threshold corresponding to theablation window length2172. If the time delay is less than the threshold, this indicates that the front face of thetissue280 lies within thewindow length2172. The receiver can indicate this by a display means, for example lighting a ‘green’ display. If the receiver detects the echo arriving later than the time threshold, then a ‘red’ display can be lit indicating that thegap282 is too large, and a lesion may not be created in the tissue.
• The use of the above information in an actual clinical setting is depicted inFIG. 31. Thecatheter100 ofcatheters2110 and2112 is introduced into the atrial chamber through theguide sheath2118. Thepositioning wires2128 and2130 are advanced in to the two left pulmonary veins LPV1 and LPV2. In the diagnostic mode, as theouter catheter2112 is rotated in amanner2124, thehousing2114 at the tip of thetherapy catheter2110 rotates in the atrial chamber. When the catheter is in position A near the LPV1, theablation window2172 intersects with thetissue wall302. This indicates a condition that the ablation of the tissue in its entire thickness can be achieved and is indicated by a ‘green’ light. As thehousing2114 continues to sweep the atrial chamber, it reaches position B near the LPV2. Here theablation window2172 does not intersect thetissue wall304. This indicates a condition that the tissue is either too far, or the ultrasound beam is pointed towards a structure such as a PV, or the atrial appendage, or the mitral valve opening. In this case, transmural ablation will not be achieved and a ‘red’ light will be indicated.
• It is the objective of the user physician to establish a contiguous beam path2176 (ref.FIG. 19) indicated by the ‘green’ light continuously lit during the movement along the entire intended lesion path. A check for this continuous green light, before energizing the ultrasound transducer, will insure that the proposed path will result in a contiguous ablation zone in the atrial wall. The situation shown inFIG. 31 does not yield a contiguous beam path, therefore the physician would move thecatheters2110 and/or2112 and sweep another circle of thehousing2114 in diagnostic mode to arrive at a situation such as that shown inFIG. 19. Once suchcontiguous path2176 is established in the diagnostic mode, the physician can proceed with the ablation of the said path using the ablation mode.
• As an added safety feature, the system can regularly, on a time-shared basis, convert from ablation mode briefly to diagnostic mode. In this way, the correct gap can be checked even during the ablation. If the red light goes on, the system will automatically exit the ablation mode, until a correct gap (i.e. green light) is again detected. Then the ablation mode will be automatically resumed. This diagnostic sampling can occur at a relatively fast sampling frequency. In the current invention, it occurs at about 40 kHz, corresponding to the duty cycle repetition rate for the diagnostic power generator. Conversely, if the ‘green’ light remains lit throughout the movement along entire ablation path, then a contiguous lesion has been created. This measure off goodness can result in an additional display (flashing ‘green’ light, for example) to inform the physician that he has created a complete contiguous lesion.
• Furthermore, since the wall thickness and the lesion depth can also be checked in the diagnostic mode on a time-shared basis during the ablation, the system can dynamically control the lesion depth by varying the sweep rate along the intended ablation path, and/or changing the power provided from the generator. In this way the lesion is even more likely to be transmural contiguously all along the lesion path. In addition, the system can minimize the possibility of creating a lesion beyond the atrial wall. If the system detects the lesion extending beyond the outer wall, the generator will be turned off. Alternatively, the system can be configured such that the generator is turned off when the depth of the lesion reaches or exceeds a preset depth.
• The above description of the design and construction of the catheter set100 is aimed at creating the ablation zone for the left pulmonary veins. A different catheter set is used for the right pulmonary veins, essentially of the same functioning principles but of a different geometry appropriate for the anatomical location of the right pulmonary veins in the left atrium of the heart. This catheter set400 is shown inFIG. 32. Theouter catheter412 has a preset shape of a ‘shepherd's hook’ so as to point towards the right pulmonary veins when placed in the atrial chamber. Thecatheter412 can move in the axial direction in theguide sheath418 in amanner420. Thetherapy catheter2410 moves inside theouter catheter412 in the axial direction in amanner2452. In addition,catheter412 can rotate in amanner424. A lumen426 (not shown) in thecatheter2410 is used to house thepositioning wires428 and430 which exit from the said lumen at thenotch427. Thecatheter2410 can also be rotated in thecatheter412 in amanner456. The distal tip portion of thecatheter2410 can be bent by means of a pull wire (not shown) in themanner454. The distal tip of thecatheter2410 is composed of a ‘castle head’housing414 which contains theultrasound transducer416. The transducer has anablation window2472 similar to the ablation window2172 (ref.FIG. 19) ofcatheter2110. The additional construction of the elements of thecatheter2410 are identical to those of thecatheter2110 as described earlier in this specification. In addition, the catheter set400 engages with theconsole2132 in a similar manner as the catheter set100.
• Under the current state of knowledge, certain ablation lines are drawn in the atrium around the pulmonary veins in an attempt to block the conduction of aberrant electrical signals. This set of ablation lines is called a lesion set. In this invention, it is proposed to have a lesion set as shown inFIG. 33. Oneablation ring306 encircles the two left PV's and anotherablation ring308 encircles the right PV's. An ablation line3310 is drawn joining the ablation rings306 and308. Finally, anotherablation line312 is drawn intersecting the ablation line3310 and down to the annulus of the mitral valve (MV).
• Next, a method for the use of the device of this invention in a clinical setting is presented as follows:
• 1. Referring toFIG. 18, position theguide sheath2118 across the atrial septum S using the conventional femoral vein approach. One technique for this procedure is described by Gill (J. S. Gill, How to perform pulmonary vein isolation, Europace 2004 6(2):83-91).
• 2. Pre-load thepositioning wires2128 and2130 in thelumen2126 of theouter catheter2112 such that the distal tips of the wires are entirely inside thelumen2126.
• 3. Advance the catheter set100 through theguide sheath2118 into the atrial chamber.
• 4. Advance one of thepositioning wire2128 through theopening notch127 of theouter catheter2112. The conical spring likeshape194 of the wire will now deploy. Under conventional fluoroscopic guidance, position the wire in the pulmonary vein LPV1. The wire can be rotated gently to help it find and navigate the ostium and the opening of the pulmonary vein. Advance the wire slightly beyond themarker129 at the proximal end to ensure its position inside the LPV1 then lock it in position using thelever2136.
• 5. Advance thesecond positioning wire2130, and guide itsconical spring196 into to second vein LPV2 in a similar manner., positioning it beyond themarker131 at its proximal end and lock in position using thelever2138.
• 6. Referring toFIG. 34, move theouter catheter2112 and theinner catheter2110 to the most proximal position in the atrial chamber. Using thetransducer2116 in a diagnostic mode, rotate the outer catheter2112 (either manually or using the motor drive of console2132) in the chamber. The generator/receiver will sense for the position of the atrial wall tissue and indicate appropriately with a green or a red light.
• 7. If the red light indication exists in a portion of the rotation, use the linear or bending motions of thecatheters2112 and/or2110 to achieve a complete green circle. At this point, acontiguous beam path2176 has been established. In the diagnostic mode, the navigation through a circle is quite rapid and can be completed in several seconds. Since the circular movement can not continue in one direction only, reverse the direction of rotation after a rotation of 360 degrees plus an overlap of about 10 to 15 degrees. If the physician chooses for the motor drive to achieve this function, the drive unit is programmed to automatically reverse the direction after a complete circle plus an overlap.
• 8. Energize the transducer in the ablation mode and start the rotary motion of thecatheter tip housing2114 using the motor drive in theconsole2132. This movement is much slower, and will typically take several minutes to complete. Confirm that the green light stays green through the entire movement.
• 9. If the red light persists over a portion of the circle, proceed with the ablation in the green zone, and later cover the red zone ablation in the following manner:
• • a. The physician can use the other linear and bending movements of the catheters to establish a path in a set of other planes which would yield a green path covering the region where the original red arc appeared.
  • b. The computer in the generator/receiver can memorize this complex green path, and upon activation, can establish an ablation zone in the tissue which is contiguous with the original green zone.
• 10. The ablation around the two left pulmonary veins LPV1 and LPV2 is now complete as shown ascurve306 inFIG. 34.
• 11. Next, theablation lines3310 and312 ofFIG. 33 are created using a method as shown inFIGS. 35A, 35B,35C, andFIG. 36.
• 12. Starting at the position of thetip housing2114 of thecatheter2110 at the end point of the just completed ablation ring306 (FIG. 34), orient thetip2114 posteriorly in the atrium using theorientation markers2166 and2168 (ref.FIG. 18) on the proximal ends of thecatheters2110 and2112.
• 13. Advance thecatheter2112 distally towards the LPV1 a few millimeters to establish thestarting point324 of the ablation line3310.
• 14. Using the diagnostic mode, move thecatheter2112 towards the right pulmonary veins in amanner314 by pulling it into theguide sheath2118. At the same time, bend the tip of thecatheter2112 in amanner316. If necessary, move thetherapy catheter2110 inside theouter catheter2112 in amanner318, and bend the tip of thetherapy catheter2110 in amanner320. All these movements are carried out to establish the locus of theablation window2172 in the ‘green’ region. Generally, this locus will be achieved by a combination of various movements of thecatheters2110 and2112 and can be carried out by the computer in the generator/receiver. Thefinishing point326 of this ‘green’ line is intended to be past the ostium of one of the right pulmonary veins. Once this horizontal green line3310 is established, the computer can memorize the actual motions required therefor.
• 15. Follow through with the formation ablation line3310 (FIG. 33) by moving thetip2114 in the ablation mode all the while maintaining the ‘green’ light. The successive positions of theablation window2172 and the resulting ablation line is shown in the top view of the atrium inFIGS. 35B and 35C.
• 16. When the catheter tip is at its most proximal position, an ablation zone around the right pulmonary veins can be created as follows:
• • a. In diagnostic mode, rotate thecatheter2112 in amanner2124 to establish a ‘green’ curve around the right pulmonary veins. Other available motions of the catheter set100 can be utilized to establish a ‘green’ curve.
  • b. Once the ‘green’ curve is established, using the ablation mode, create theablation zone308.
• 17. Now referring toFIG. 36, move thetip2114 of thecatheter2110 to an approximately middle position of the ablation line3310, and a few millimeters clockwise (i.e. above the line3310) to establish the startingposition328 for thevertical ablation line312, as shown inFIG. 33.
• 18. Using the catheter in the diagnostic mode, rotate thecatheter2112 counterclockwise in themanner2124, and ensure a ‘green’ path is established. Theend point330 of thisline312 is at the mitral valve annulus which can be detected by the transducer by virtue of the movements of the leaflet of the valve itself. If required, additional movements of the catheters can be used as appropriate to determine the locus of the ‘green’ line. Once this ‘green’ line is established, enable the computer to memorize the required movements.
• 19. Using the transducer in the ablation mode, form anablation line312 from thehorizontal line2110 down to the annulus of the mitral valve (MV).
• 20. Withdraw the positioning wires into the lumen of thecatheter2112 and withdraw the catheter set100 from the body of the patient through theguide sheath2118 while leaving the saidguide sheath2118 in position across the septum.
• 21. The ablation zone encircling the right pulmonary veins is made using a different catheter set specifically designed for that anatomy of the region of the atrium.
• 22. Referring toFIG. 37, advance theouter catheter412 distally until itscurved surface498 is in contact with the inside left wall of the atrium.
• 23. Place thepositioning wires428 and430 in the lumen426 (not shown) of the catheter using the technique described earlier.
• 24. Position thewires428 and430 into the right pulmonary veins using the technique described earlier.
• 25. Advance thetherapy catheter2410 to its most distal position. Using the diagnostic mode, rotate thetip housing414 of thecatheter2410 in themanner456. Look for the presence of the ‘green’ circle.
• 26. If the ‘green’ circle is not established, move the catheter2410 a few millimeters proximal in themanner2452 and repeat step25. Repeat this step26 until a ‘green’ circle is established.
• 27. Now energize the transducer in ablation mode, and create the lesion308 (FIG. 33).
• 28. If the ‘red’ light appears, follow the procedure in step9 above.
• 29. The formation of the rightPV ablation zone308 is now complete.
• 30. Retract thepositioning wires428 and430 from the atrium by withdrawing them through the lumen of thecatheter412.
• 31. Remove the catheter set400 from the atrium through theguide sheath2118.
• 32. Remove theguide sheath2118 from the heart and follow the conventional closure technique for the femoral vein.
• The procedure above describes the formation of one lesion set. As the catheter sets100 and400 are provided with multiple degrees of motions, the physician can create a variety of other lesion sets to achieve a conduction block.FIG. 38 shows some of the lesion sets which can be created with the device of the present invention. The possible lesion sets are not limited to those presented here, and it is important to recognize that the device of this invention allows the physician to create any other lesion set in the atrium of the heart.
• In a conventional catheter-based ablation procedures, the physician check the presence or absence of the conduction block by mapping of the atrial tissue. The technique involves checking the electrical conduction between the pulmonary veins and the other parts of the atrial wall on the endocardial side. Thewires428 and430 are already positioned inside the pulmonary veins and can be easily used as electrodes for the sensing and mapping purposes. The electrical connections to thepositioning wires428 and430 are provided at theconsole2132.
• This specification for the present invention discusses an ultrasound transducer as a single element in the shape of a disc mounted at the end of a cylindrical catheter. This invention is not intended to be limited to the use of a single element circular disc. A rectangular or oval shaped transducer can be mounted on the cylindrical side of the catheter tip. Appropriate fluid flow mechanism can be provided to cool the said transducer and to provide for the separation of the surrounding blood from the surface of the transducer. In addition, the transducer configuration is not intended to be limited to that of a disc. The transducer can be in the form of an array of multiple transducers. The transducer can also be fabricated as a set of concentric circles (known in the art as an annular array), for example, instead of the single element disc described in this invention. One skilled in the art will appreciate the wide possibility of possible shapes, sizes, and configurations which can be used for the transducer in this invention.
• This specification of the present invention discusses the use of aconsole2132 that allows simple control of the catheter sets100 and400. This invention is not intended to be limited to the use of this console. The catheter sets, with appropriate modifications, can also be controlled and manipulated by other means, for example mechanical robotic or magnetic controllers with remote user interfaces that manage all motions, with or without haptic feedback.
• In some embodiments, the tip of the treatment catheter and the anchor can both be made of metal and can communicate electrically with the control system so that they can serve as mapping electrodes for determining the electrical characteristics of the heart tissue.
• The description above of the device of this invention has been limited to the treatment of atrial fibrillation in the left atrium of the heart. However, the device, with appropriate modifications, can be used in other parts of the body. For example, if it is determined that the right atrium is also involved in the condition of atrial fibrillation, appropriate lesion set can be created in the wall of the right atrium as well. Another example is the use of another version of the device in the ventricular space for the treatment of ventricular arrhythmia. The transducer creates an ultrasound beam which is capable of creating transmural lesions in the myocardial tissue, and this beam can be moved around in the chambers of the heart to create intended lesions in the wall of the heart.
• While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention.

Claims (40)

1. A cardiac ablation method comprising:

inserting a treatment catheter into an atrium of a heart, the treatment catheter comprising an ultrasound emitter;

positioning the ultrasound emitter to face heart tissue within the left atrium outside of a pulmonary vein;

emitting ultrasound energy from the ultrasound emitter while rotating the ultrasound emitter about a rotation axis; and

ablating heart tissue with the ultrasound energy to form a lesion outside of a pulmonary vein.

2. The method ofclaim 1 wherein the positioning step comprises bending an ultrasound emitter support.

3. The method ofclaim 1 wherein the positioning step comprises moving the ultrasound emitter parallel to the rotation axis.

4. The method ofclaim 1 wherein the positioning step comprises anchoring the treatment catheter.

5. The method ofclaim 4 wherein the anchoring step comprises placing an anchor against an atrial wall outside of a pulmonary vein.

6. The method ofclaim 4 wherein the anchoring step comprises placing an anchor within a pulmonary vein.

7. The method ofclaim 4 wherein the anchoring step comprises placing a plurality of anchors within a plurality of pulmonary veins.

8. The method ofclaim 4 wherein the anchoring step comprises expanding an anchor within a support catheter.

9. The method ofclaim 4 wherein the rotating step comprises rotating the treatment catheter about the anchor.

10. The method ofclaim 1 wherein the rotating step comprises rotating the ultrasound emitter less than 360° around the rotation axis.

11. The method ofclaim 1 wherein the rotating step comprises rotating the ultrasound emitter at least 360° around the rotation axis.

12. The method ofclaim 1 wherein the ablating step comprises forming a lesion encircling at least two pulmonary vein ostia.

13. The method ofclaim 12 wherein the lesion is a first lesion, the method further comprising forming a second lesion around two other pulmonary vein ostia.

14. The method ofclaim 13 further comprising forming a third lesion extending from the first lesion to the second lesion.

15. The method ofclaim 14 further comprising forming a fourth lesion extending from the first, second or third lesion substantially to a mitral valve annulus.

16. The method ofclaim 1 wherein the emitting step comprises transmitting ultrasound energy distally from a distal end of the treatment catheter.

17. The method ofclaim 1 wherein the emitting step comprises transmitting ultrasound energy radially from the treatment catheter.

18. The method ofclaim 1 wherein the emitting step comprises transmitting ultrasound energy from an ultrasound transducer and reflecting the ultrasound energy from a reflector.

19. The method ofclaim 18 wherein the rotating step comprises rotating the reflector.

20. The method ofclaim 18 wherein the transmitting step comprises transmitting the ultrasound energy in a proximal direction.

21. The method ofclaim 1 further comprising passing fluid through the ablation catheter and through an exit port adjacent the ultrasound emitter.

22. The method ofclaim 21 further comprising passing fluid into a fluid chamber disposed between the ultrasound emitter and the heart tissue.

23. The method ofclaim 1 further comprising sensing distance between the ultrasound emitter and a tissue surface.

24. The method ofclaim 23 wherein sensing distance comprises using the ultrasound emitter to sense distance between the emitter and the tissue surface.

25. The method ofclaim 23 wherein sensing distance comprises sensing distance between the ultrasound emitter and the tissue surface over an intended ablation path prior to the ablating step.

26. The method ofclaim 25 further comprising repositioning the ultrasound emitter as a result of sensed distance determined in the sensing step.

27. The method ofclaim 1 further comprising sensing depth of ablation in the heart tissue.

28. The method ofclaim 27 wherein sensing depth of ablation comprises using the ultrasound emitter to sense depth of ablation in the heart tissue.

29. The method ofclaim 27 further comprising controlling a speed of rotation of the ultrasound emitter based on sensed depth of ablation.

30. The method ofclaim 27 further comprising controlling power delivered to the ultrasound emitter based on sensed depth of ablation.

31. The method ofclaim 1 further comprising sensing thickness of the heart tissue.

32. The method ofclaim 31 further comprising controlling a speed of rotation of the ultrasound emitter based on sensed thickness of heart tissue.

33. The method ofclaim 31 further comprising controlling power delivered to the ultrasound emitter based on sensed thickness of heart tissue.

34. The method ofclaim 1 wherein the ablating step comprises forming a substantially elliptical lesion segment in the heart tissue.

35. A cardiac ablation method comprising:

inserting a treatment apparatus into an atrium of a heart, the treatment apparatus comprising an ultrasound emitter and an ultrasound emitter support;

positioning the ultrasound emitter to face heart tissue within the left atrium outside of a pulmonary vein;

emitting ultrasound energy from the ultrasound emitter while changing a bend angle in the ultrasound emitter support; and

ablating heart tissue with the ultrasound energy to form a lesion outside of a pulmonary vein.

36. The method ofclaim 35 wherein the positioning step comprises bending an ultrasound emitter support.

37. The method ofclaim 35 wherein the positioning step comprises anchoring the treatment catheter.

38. The method ofclaim 35 further comprising rotating the ultrasound emitter about a rotation axis during the emitting step.

39. The method ofclaim 35 wherein the ablating step comprises forming a substantially linear lesion in the heart tissue.

40. The method ofclaim 35 wherein the ablating step comprises forming a substantially elliptical lesion segment in the heart tissue.

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